Lighting in Reef Tanks feature: Questions

[delbeek]

Interesting article Mike, I had a few questions and comments:

1. I would like to see you compare the amount of light fall off between the various tanks that use metal halide and those that use PC/FL lighting only. You would have to normalize for depth and wattage. I think you may find that the % of light loss with PC/FL lamps will be less than with MH. Hopefully you can test this with the data you have.

2. It is very sobering to see how quickly PAR drops over such a short depth. You went from 1200 at the surface down to 230 at the bottom thats like going from the 12 ft here in HI to over 100 ft, and people wonder why their corals bleach when they move them a few inches up or move their lights a few inches down. 8O

3. I am a little confused by your use of the Apogee PAR meter both above and below the water. My understanding is that you need to use a correction factor or the probe has to be calibrated to be used underwater, you can't just move the probe in and out of the water to take readings. Can you comment on this?

4. I am not sure how you derived the PAR values for the different depths based on transmittance in one meter. Its a logarithmic conversion due to the inverse square law of light fall-off. I think your values are too low. For example, at 10 meters (which is close to 30 ft) you derive values of 621 and 568 for 1A and 1B. Measured figures I have from a couple of different sources in Hawaii, the Caribbean, Indonesia and off Australia show values closer to 1000.

5.

"On the other hand, it is also very possible that some of the pigmentation that we see is due to too much light. Once a coral reaches P-max, more light actually lowers the rate of photosynthesis slightly. So a safer approach might be to look at lowering the light levels somewhat."

I am not sure I follow your logic here. Lowering light will reduce pigments? I would think these are the pigments you WANT to have i.e. the colored ones. Lowering the light will bring you closer to Pmax but may result in less colorful corals. Even if you lower the rate of photosynthesis somewhat by having higher light, I don't think it is that critical to always be running it at maximum rate, this is not the case in nature due to the way light behaves on a reef increasing and decreasing over the course of the day. In our aquariums with most people running their maximum light levels 8-10 hours a day and, perhaps, running photosynthesis at its maximum over the same time period, I would argue that lower the rate might be beneficial.

In other words, shoot for whatever are the minimum levels required to keep the higher light loving species alive and thriving. We don’t really know these levels for coral, but we do know what works for Tridacna clams. It would seem that shooting for levels of approximately 250 μE/m2 at the bottom of your tank should allow you to keep Tridacnas. Thus, it seems fairly safe to say that many, if not most, other light-loving species should survive just fine under this level of light.

Mmm ... again I don't see the logic in this, your coral and clams will be less colorful. Depending on the species of clam, 250 seems rather low for say T. crocea and T. maxima that are usually found in shallow waters (<20 ft)where PAR can easily reach levels of over 1000.

Aloha!
JCD
[/quote]

 

[mkirda]

Interesting article Mike, I had a few questions and comments:

1. I would like to see you compare the amount of light fall off between the various tanks that use metal halide and those that use PC/FL lighting only. You would have to normalize for depth and wattage. I think you may find that the % of light loss with PC/FL lamps will be less than with MH. Hopefully you can test this with the data you have.

Well, Charles, I have collected a good deal more data on tanks, and a followup article should appear after I present the data at BAS in September.

This will end the work on existing tanks, but lead to a different testing regime using bare tanks and a jig to hold the lights and the sensor in position. This is where I suspect your question can really be adequately addressed. PM me if you want more details or if you are willing to provide input.

2. It is very sobering to see how quickly PAR drops over such a short depth. You went from 1200 at the surface down to 230 at the bottom thats like going from the 12 ft here in HI to over 100 ft, and people wonder why their corals bleach when they move them a few inches up or move their lights a few inches down. 8O

The differences in the light field are incredible. Last night I was measuring under a new 175W Ushio bulb. Smack dab underneath was like 1400, but move it off toward the mogul base about one inch, the numbers were more like 800. 8O Moving the sensor an inch can result in the light field doubling in certain instances...

3. I am a little confused by your use of the Apogee PAR meter both above and below the water. My understanding is that you need to use a correction factor or the probe has to be calibrated to be used underwater, you can't just move the probe in and out of the water to take readings. Can you comment on this?

Can I ask where you got this impression? I have never heard of a correction factor needing to be used above and below the water...

These measurements were fairly crude- The sensor was placed on probe, then placed directly underneath the bulb, but above the water surface. The probe is held as steady as humanly possible and the PAR noted down. Next the probe is lowered slightly, just enough for the water to get over the surface of the sensor. Again it is held steady and the values noted.

The very act of moving the sensor down will change the light level. However, in testing the values of say 1/4" above the water surface vs. 1/8" above the water surface, the difference in the light field was negligable. When I tried to figure the numbers out, they seemed to be maybe 10 - 20 mE/m2 difference. So most of the difference can be accounted for by reflection off the surface of the water.

In doing the next phase, I intend to refine this somewhat as I can keep the sensor steady and vary the water height instead. This should allow for far more precise measurements.

4. I am not sure how you derived the PAR values for the different depths based on transmittance in one meter. Its a logarithmic conversion due to the inverse square law of light fall-off. I think your values are too low. For example, at 10 meters (which is close to 30 ft) you derive values of 621 and 568 for 1A and 1B. Measured figures I have from a couple of different sources in Hawaii, the Caribbean, Indonesia and off Australia show values closer to 1000.

Could you PM with the references? I'd like to pull them.

Is it possible I made a mistake on the table? Yes, I suppose it is possible.
In order for me to check it out, I'll have to get the book back on ILL.

I will request it today and try to get back to you later on this point.

5.

"On the other hand, it is also very possible that some of the pigmentation that we see is due to too much light. Once a coral reaches P-max, more light actually lowers the rate of photosynthesis slightly. So a safer approach might be to look at lowering the light levels somewhat."

I am not sure I follow your logic here. Lowering light will reduce pigments? I would think these are the pigments you WANT to have i.e. the colored ones. Lowering the light will bring you closer to Pmax but may result in less colorful corals. Even if you lower the rate of photosynthesis somewhat by having higher light, I don't think it is that critical to always be running it at maximum rate, this is not the case in nature due to the way light behaves on a reef increasing and decreasing over the course of the day. In our aquariums with most people running their maximum light levels 8-10 hours a day and, perhaps, running photosynthesis at its maximum over the same time period, I would argue that lower the rate might be beneficial.

In other words, shoot for whatever are the minimum levels required to keep the higher light loving species alive and thriving. We don’t really know these levels for coral, but we do know what works for Tridacna clams. It would seem that shooting for levels of approximately 250 &#956;E/m2 at the bottom of your tank should allow you to keep Tridacnas. Thus, it seems fairly safe to say that many, if not most, other light-loving species should survive just fine under this level of light.

Mmm ... again I don't see the logic in this, your coral and clams will be less colorful. Depending on the species of clam, 250 seems rather low for say T. crocea and T. maxima that are usually found in shallow waters (<20 ft)where PAR can easily reach levels of over 1000.

Charles, this is where I hedged my bets...

It seem amongst aquarists there are two schools of thought:
1) Recreate a noon time reef flat by blasting as much light as possible. In other words, more is better.
2) Give them what they need to survive, and let them get the rest from food.

I've read Eric Borneman's comments a number of times on how PMax is all you want to shoot for. PMax is also likely unknown for most of the species we keep- Either that or I've been looking in all the wrong places... :wink:

Seeing very successful reef tank systems under various lighting regimes and various lighting levels, one thing is clear to me: Corals have the ability to adapt to a degree most of us never thought possible.

In the end, what I tried to say was that the truth seems to be between the two schools of thought. That you can blast your corals with light if you want to. And that you can lower the light levels somewhat if you want to.
In the end, it still seems to me that if you are wanting a higher-light loving coral tank, then you should shoot for PAR levels of around 250 at the bottom of your tank. This ensures levels of around 1000 at the top, and various levels underneath.

How they want to achieve that is up to the tank owner.

I still believe that coral coloration, if I had to chalk it up to one or two things, is mostly influenced by light intensity and calcium/alkalinity levels.
I think it remains to be seen if spectrum has much influence besides our eye's perception of color.

I hope I answered everything satisfactorily, Charles. If you have more questions, or I left anything out, please feel free to ask me in more detail.

Regards.
Mike Kirda

 

[delbeek]

Well, Charles, I have collected a good deal more data on tanks, and a followup article should appear after I present the data at BAS in September.

This will end the work on existing tanks, but lead to a different testing regime using bare tanks and a jig to hold the lights and the sensor in position. This is where I suspect your question can really be adequately addressed. PM me if you want more details or if you are willing to provide input.

Actually I made a typo in my first email, I meant that the PC/FL would penetrate LESS than the MH. I don't think you need to get that elaborate, statistics can handle what you have so far and can normalize the results by cancelling out wattage and depth differences. I think Dana Riddle has done a lot of what you are proposing and Sanjay Joshi too, so you might want to contact them about proper setup.

Can I ask where you got this impression? I have never heard of a correction factor needing to be used above and below the water...

These measurements were fairly crude- The sensor was placed on probe, then placed directly underneath the bulb, but above the water surface. The probe is held as steady as humanly possible and the PAR noted down. Next the probe is lowered slightly, just enough for the water to get over the surface of the sensor. Again it is held steady and the values noted.

The very act of moving the sensor down will change the light level. However, in testing the values of say 1/4" above the water surface vs. 1/8" above the water surface, the difference in the light field was negligable. When I tried to figure the numbers out, they seemed to be maybe 10 - 20 mE/m2 difference. So most of the difference can be accounted for by reflection off the surface of the water.

You can not use a sensor both above and below water unless it has been calibrated for that use. This is how the LiCor sensors work, you have to purhcase either above water and below water senors. The Apogee uses a resistor to add that correction factor but it is probably air corrected since this is the most common use for it. Your underwater values are most likely inaccurate but probably by a small percentage. I don't really know, you'd have to contact Apogee and ask them about using it in both air and water, they be able to give you a correction factor you could run your data through.

The other problem with the Apogee instrument is that it is a flat 2 pie sensor, you are only measuring direct light coming down from the surface. You really need to use a 4 pie sensor that is cosine corrected for use underwater. This way you get light measurements from pretty much all directions, not just from above. Light fields in aquaria are very complicated due to reflection from the sides of the tank as well as the bottom material. Using a 2 pie sensor only gives you a partial picture of the actual light field encountered by the corals.

It seem amongst aquarists there are two schools of thought:
1) Recreate a noon time reef flat by blasting as much light as possible. In other words, more is better.
2) Give them what they need to survive, and let them get the rest from food.

I've read Eric Borneman's comments a number of times on how PMax is all you want to shoot for. PMax is also likely unknown for most of the species we keep- Either that or I've been looking in all the wrong places...

Seeing very successful reef tank systems under various lighting regimes and various lighting levels, one thing is clear to me: Corals have the ability to adapt to a degree most of us never thought possible.

You are absolutely correct when you say corals are highly adaptable, but this also applies to Pmax levels. My understanding is that this is a moving target. In other words, Pmax can change in corals depending on light intentisty. Given time, corals adapt to higher light levels and Pmax also increases. So to choose a value of 250 as what is needed to cover Pmax may be true for some corals but not all, depending on what they are used to. True, over time, those with higher values will adjust to the lower intensity and their Pmax will lower, however, I think that lowering intensity will only result in loss of color and brown corals. There is a lot that is not known about coral pigments like what they are for and how they are affected by various factors. I am not sure why you feel calcium and alkalinity are involved though. Can you explain the reasoning behind this?

Aloha!
JCD

 

[rharker]

Mike:

Charles brings up a number of issues that unfortunately compromise the value of your measurements and observations. There are a number of reasons the LiCor sensor costs over five times as much as the Apogee sensor. You dismiss these differences as inconsequential, but they are not. The unit of measurement, E/m^2/sec, assumes the light source is striking the sensor at right angles. To compensate for the fact that light might not be striking at right angles, the better sensors are "cosine corrected." That is, there is a (typically mechanical) method built into the sensor to compensate for differing angles. Denser material like water refracts light differently than air. so the cosine correction has to be different above and below the water. That's why LiCor makes both underwater and above water sensors.

The Apogee sensor and meters are fine for comparing light bulbs. I wrote as much in a review of them several years ago. There are significant problems, however, using them in other areas. You noted that the light level just below the surface of the water was just slightly lower than the light level above the surface. Since you're measuring light levels in two different media, you have to be careful about atrributing the light fall off to anything other than the media themselves. The small drop off in light could be the focussing effect of water.

A more important issue for hobbyists and a more significant flaw in your data is the use of a flat (2pi) sensor to measure light fields in a tank. With the Apogee sensor, you are measuring only the direct light falling on the sensor. There are many reflecting surfaces in a tank, and just because direct light falls off significantly doesn't mean that total intensity falls off as quickly. A better tool to explore light fields in a reef tank is a spherical (4pi) sensor. This measures light in 360 degrees, so reflected light is counted along with direct light.

Using a spherical sensor, I have measured extremely high light levels near the bottom of a reef tank. The slides of the tank and the sand apparently reflected and focussed the light in an unpredictable way. Looking at your measurements, I suspect that had you measured the entire light field in some of the locations, you would have measured considerably higher light levels. This reflected light is just as available to the animals as the direct light.

The same problem arises when you try to measure reflectors and light hoods with a flat sensor. As you move further from the light source, the angle at which light is striking the sensor is increasing. A flat sensor will show a steeper light fall off than actually occurs.

While a spherical sensor is the best tool for measuring complex light fields, you can approximate the effect by using two flat sensors, one pointing up and a second pointing down. Combining the two measurements gives you a better estimate of the total light. A cruder method that will at least demonstrate the impact is to rotate the sensor at a given point in a tank. I think you'll be surprised by the amount a reflected light in a reef tank.

Richard Harker

 

[mkirda]

You can not use a sensor both above and below water unless it has been calibrated for that use. This is how the LiCor sensors work, you have to purhcase either above water and below water senors. The Apogee uses a resistor to add that correction factor but it is probably air corrected since this is the most common use for it. Your underwater values are most likely inaccurate but probably by a small percentage. I don't really know, you'd have to contact Apogee and ask them about using it in both air and water, they be able to give you a correction factor you could run your data through.

According to Apogee, they do not think there is enough of a correction factor to be worth pursuing. As the sensors used by LiCor and Apogee differ, LiCor's may be more sensitive and in need of adjustment for this purpose. I defer to Apogee on this one.

The other problem with the Apogee instrument is that it is a flat 2 pie sensor, you are only measuring direct light coming down from the surface. You really need to use a 4 pie sensor that is cosine corrected for use underwater. This way you get light measurements from pretty much all directions, not just from above. Light fields in aquaria are very complicated due to reflection from the sides of the tank as well as the bottom material. Using a 2 pie sensor only gives you a partial picture of the actual light field encountered by the corals.

Yes and no, Charles.

You bring up a good point, but it is minimized by the way I was gathering the data, and by what I was trying to achieve here. Looking at things, I suppose that I didn't explain that well enough in the article. I've got another presentation to get finish getting ready for and this gives me some thoughts on adding this into the presentation. Suffice it to say that the way I have gathered the data, the differences between what a 2pi sensor and a 4pi sensor would have measured would be minimal.

So to choose a value of 250 as what is needed to cover Pmax may be true for some corals but not all, depending on what they are used to. True, over time, those with higher values will adjust to the lower intensity and their Pmax will lower, however, I think that lowering intensity will only result in loss of color and brown corals.

As with any choice or recommendation, you are free to disagree. I thought I had this covered when I explained that this should cover most, but not all, of the light level requirements of higher-light loving corals. Key point: NOT ALL.

There is a lot that is not known about coral pigments like what they are for and how they are affected by various factors. I am not sure why you feel calcium and alkalinity are involved though. Can you explain the reasoning behind this?

Indirectly I was agreeing with an idea Dana Riddle put forth seven or eight years back. Namely, that boosting alkalinity to around 3.5 mEQ/L while maintaining calcium levels (or boosting them slightly) will promote better coloration. Frankly, I think this has more to do with increased growth than anything else.

Sorry for the delay in responding.

Regards.
Mike Kirda

 

[mkirda]

Richard,

When I am measuring, for example, levels at the cap of a leather coral, what benefits exactly does a 4pi sensor give me?

None. Unless the leather coral itself is emitting light.

While I will agree with you that the Apogee sensor will undermeasure some, Apogee's own tech support staff indicate that the difference in the measurements will be inconsequential. Again, I defer to Apogee- they know their own sensor.

I'll post more on the methods used to gather the light levels later.

Regards.
Mike Kirda

 

[delbeek]

According to Apogee, they do not think there is enough of a correction factor to be worth pursuing. As the sensors used by LiCor and Apogee differ, LiCor's may be more sensitive and in need of adjustment for this purpose. I defer to Apogee on this one.

Perhaps, but I think this should have been stated in the text. I would think that this sort of thing would have been brought up during the article "review" process.

Yes and no, Charles.

You bring up a good point, but it is minimized by the way I was gathering the data, and by what I was trying to achieve here. Looking at things, I suppose that I didn't explain that well enough in the article. I've got another presentation to get finish getting ready for and this gives me some thoughts on adding this into the presentation. Suffice it to say that the way I have gathered the data, the differences between what a 2pi sensor and a 4pi sensor would have measured would be minimal.

I am not sure that I follow your reasoning here but will wait until you can give a better explanation.

As with any choice or recommendation, you are free to disagree. I thought I had this covered when I explained that this should cover most, but not all, of the light level requirements of higher-light loving corals. Key point: NOT ALL.

Depending on where those corals came from and what they have been subjected to your recommendation might not apply to ANY corals. My point was that sure you can keep "higher-light loving corals" at 250 but I don't think you will be too happy with their appearance. :wink:

Indirectly I was agreeing with an idea Dana Riddle put forth seven or eight years back. Namely, that boosting alkalinity to around 3.5 mEQ/L while maintaining calcium levels (or boosting them slightly) will promote better coloration. Frankly, I think this has more to do with increased growth than anything else.

Well there is some disagreement as to what Dana actually did and what he observed, suffice it to say that a rapid increase in alkalinity can cause corals to bleach, making them appear more colorful due to loss of zooxanthellae. The same thing happened in Fiji a few years back when importers in the US were crowing about all the really colorful corals coming out of Fiji .. problem was ... they had lost their zooxanthellae due to high water temps and all that remained were the underlying yellows, pinks and purples of the coral.

The only thing that I know has been scientifically shown regarding alkalinity in closed systems is that increasing alkalinity will result in continued/increased coral growth under high nitrate and phosphate levels. It helps to explain why so many people can grow corals in their home aquaria despite having 100X natural levels of nitrogen in their system.

The problem I have with that is, increasing coral growth often results in much lower density skeletons that can be easily crushed to dust in your fingers.

Anyway I liked what you did, the questions I have had are more a reflection of the types of clarifications I would have asked had I reviewed it before publication.

Aloha!
JCD

 

[rharker]

When I am measuring, for example, levels at the cap of a leather coral, what benefits exactly does a 4pi sensor give me? None. Unless the leather coral itself is emitting light.

Actually Mike, the leather doesn't have to emit light, it just needs to reflect it. Every non-black surface on a reef and in a tank reflects light to some degree, so the things around the leather impact the amount of light the leather is receiving. Unless one has measured light coming from all directions, one hasn't fully characterized intensity in a complex light field.

Apogee's own tech support staff indicate that the difference in the measurements will be inconsequential. Again, I defer to Apogee- they know their own sensor.

They may know their sensor, but how many on their technical staff have measured light on a coral reef or even a reef tank? How many on their staff have used a 4pi sensor? If the differences were inconsequential, why would every manufacturer of underwater sensors make a 4pi sensor? Measuring terrestrial and underwater light fields is quite different. The sun is a point source and a cosine corrected 2pi sensor is all one needs on land. Water is another story. Diffusion, diffraction, and reflection all complicate matters. Despite Apogees assurances to the contrary, "some real data" would be based on readings from the entire light field, not just direct light.

Richard Harker

 

[rharker]

You can not use a sensor both above and below water unless it has been calibrated for that use.

Charles, some rough calculations suggest that there are other more serious errors associated with the Apogee sensor. Traceable sensors like LiCor's are nearly flat with a slight roll-off in sensitivity close to 400 nM. The Apogee is far from flat. Sensitivity is only 30% at 400 nM and nearly 120% close to 650 nM. In other words, it is fairly insensitive to blue light and overly sensitive to yellow light. The impact becomes clear if we try to compare two bulbs with very different color temperatures. A low Kelvin bulb's PAR will be over stated while a high Kelvin bulb's PAR will be understated. The error could be rather large. Using a LiCor sensor, a 5500K and 20,000K bulb might both measure 500 uE/m^2/sec, but the Apogee might measure 600 uE for the 5500K and 350 uE for the 20,000K. That discrepancy would overwhelm any diffraction error.

The readings in tanks using high Kelvin bulbs are probably understated by a significant margin.

Richard Harker

 

[mkirda]

...might... and ....might... being the operative words here.

My point to you, Richard, is that this is not a definitive, be-all, end-all study.
This is merely the beginning.

To say that no one can do any level of work without a $5000 device basically tells the hobbyists to "just leave it to the experts". Sorry if I disagree with that assessment.

While I agree that it would be better to have data from the Licor sensor, the fact is that: 1) Very few of us can afford one, and 2) I'm never going to spend that kind of cash to settle this argument, unless I happen to hit Lotto.
It just isn't worth $5000+ to me.

I wish I had the time to write now how the data was gathered, but I can't do it right now. If you are at MACNA, let's hook up and we can talk your points over.

I have spoken to Sanjay Joshi about sending him my meter and having him try some measurements, comparing the Licor sensor to Apogee's. It is likely that we can find a decent fudge-factor to address the kelvin rating concerns you bring up, at least for in-air readings. I don't believe he has a 4pi u/w sensor for it though, and doubt that he'd fork out the thousands required for it either.

Later.
Mike Kirda

 

[delbeek]

Mike: Where did you get the $5000 figure from? We purchased a LI-1000 datalogger and spherical U/W sensor and 3 m of cable for about $1500 in 1998 from LiCor. You can get the u/w sensor for about $300 I think and the basic LI-250 light meter for much less than teh LI-1400 datalogger. OKay so still more than the Apogee unit but not $5000! :lol:

When you measured the light levels were all the pumps and powerheads turned off?

Aloha!
Charles

 

[rharker]

...might... and ....might... being the operative words here. My point to you, Richard, is that this is not a definitive, be-all, end-all study. This is merely the beginning.

Mike, the "might" refer to the size of the error, not the fact that potentially significant errors are introduced by the sensor's insensitivity to shorter wavelengths. There's no question that higher Kelvin bulbs are going to read low, it is just that each brand of bulb is going to have a different amount of error. I've pointed this out in previous articles on using inexpensive light meters, so this shouldn't have been unexpected.

I understand that this article is just the beginning, but one doesn't normally publish potentially faulty data and then fix it in later articles. A better approach is to acknowledge up-front the potential limitations of the data and try to compensate for the limitations. An example of that approach is my original Aquarium Frontiers PAR article in 1997. where I demonstrated that lower Kelvin bulbs produce more short wavelength light than higher Kelvin bulbs. At the time I didn't have a spectroradiometer, so taking an approach first applied in developing underwater spectroradiometers, I utilized filters and noted the limitation of the approach.

I explained my procedure and then justified the procedure by providing references to scientific articles that used the same technique. I note that your article included no references. The purpose of references is to demonstrate that you are familiar with the literature on the subject and that your methods and procedures are consistent with previous work. If you choose to diverge from previous work, it also gives you an opportunity to explain why you've chosen to go a different way.

Perhaps titling this first article, "Some real data" was a bit optimistic. "Some preliminary data" would have been a little more accurate. Also readily acknowledging the potential errors rather than dismissing them would have been a better course of action. I look forward to follow up articles.

Regard,
Richard Harker

 

[wooglins]

I have a question about my Hamilton Fixture. I have the hamilton 48inch fixture that includes 2 175watt MH bulbs (bulbs are 10k xm's), and 2 x 40 watt URI Actinics. The reflector is simply the reflective white material. I called hellolights to order some reflectors from them to retrofit into the Hamilton, and they talked me out of it. They said they are a divsion of a company that does reflector testing, and that I would not get more than a 10% increase if that much in light intensity in the tank. This was coming for the company I was attemptining to purchase 80 dollars worth of reflectors from.

1. Should I add refectors to the hamilton fixture? Is it worth it?
2. What do you think about what hellolights says?
3. How much light dropoff do you get based on how high your lights are above the water? I would think that the light loses less intensity thru air, than thru water.


The fixture I have is here:

http://www.hamiltontechnology.com/shop/ ... b815dad88b

 

[mkirda]

would not get more than a 10% increase if that much in light intensity in the tank. This was coming for the company I was attemptining to purchase 80 dollars worth of reflectors from.

1. Should I add refectors to the hamilton fixture? Is it worth it?
2. What do you think about what hellolights says?
3. How much light dropoff do you get based on how high your lights are above the water? I would think that the light loses less intensity thru air, than thru water.


The fixture I have is here:

http://www.hamiltontechnology.com/shop/ ... b815dad88b

Actually, I would say that they are probably right - going from white to reflective aluminum will do little in a flat reflector.

The problem lies in their lighting fixture design. To really improve the light llevels, you need to add a true reflector to it. See something like a SpiderLight or LumenArc 3 reflector to see what I mean. The Hamilton fixture just isn't wide enough to accommodate one of these.

1. No.
2. They are correct, IMO.
3. The amount of intensity is inversely proportional to the distance from the bulb. The further away, the more intense the fall-off. I have seen huge differences in light levels at the bottom of a tank just by lowering a fixture from 12" to 6" from the water. Light levels can literally double.

Honestly, I'd look at another fixture.

Regards.
Mike Kirda

 

[wooglins]

I added some PFO parabolic refelctors to the Hamilton hood no problem. They fit right in, and just from appearance it looks like the light output has doubled. Best part was the price, they were only 22.00 each.

 

[RicardoMiozzo]

Well there is some disagreement as to what Dana actually did and what he observed, suffice it to say that a rapid increase in alkalinity can cause corals to bleach

Dear Charles,
Why could this happen ?

 

[RiddleLabs]

Aloha Ricardo,

Perhaps I can save Charles the trouble of being the middleman, and relay my observations.

While working at Aquatic Wildlife a few years ago, we raised the alkalinity level dramatically by addition of a commercially available buffer. The next day, we noticed one of the broodstock corals (tentatively ID'd as Acropora millepora) had turned from brownish to brick red. This was the only coloration change noted in the 1,200 gallon system that contained ~2,000 corals.

I had a theory that the increase of bicarbonate (as a source of inorganic carbon for photosynthesis) may have 'turbo-charged' photosynthesis. However, recent experiments using a PAM fluorometer have not confirmed that this was the case. Exactly why the A. millepora demonstrated such a dramatic, overnight change in coloration is still a mystery.

I'd like to hear Charles' thoughts as well.

Dana

 

[RicardoMiozzo]

My doubt is simply why.
I have observed high levels of alkalinity apparently related to corals more colorfull. Not with one specie in particular, but in general, since I have the opportunity of seeing several aquaria and testing alk, Ca++, etc of their water.
What caused me interested in is the fact that I have always been very positive in the sense that there is no reason at all to mantain alk, Ca++ or any other water component at levels higher than those found in Nature.
I only noticed that, like Charles says, "boosting" alk makes coral skeleton more fregile than normal.
So, if Charles could tell me why this happens, I'd be happy to learn something I don't know, and also confirm some of my thoughts.

 

[delbeek]

My doubt is simply why.
I have observed high levels of alkalinity apparently related to corals more colorfull. Not with one specie in particular, but in general, since I have the opportunity of seeing several aquaria and testing alk, Ca++, etc of their water.
What caused me interested in is the fact that I have always been very positive in the sense that there is no reason at all to mantain alk, Ca++ or any other water component at levels higher than those found in Nature.
I only noticed that, like Charles says, "boosting" alk makes coral skeleton more fregile than normal.
So, if Charles could tell me why this happens, I'd be happy to learn something I don't know, and also confirm some of my thoughts.

Suddenly raising alkalinity and maintaining a high alkalinity are two different matters. Suddenly increasing alkalinity is a rapid change in water chemistry that can stress the coral and could lead to bleaching.

Rapid coral growth brought on by high Ca and alk levels will lead to less dense skeletons since they are laying down skeleton very quickly. Why this is I don't know, but I have also seen this happen at low levels of alkalinity too.

Aloha!
Charles

 

[John_Brandt]

While working at Aquatic Wildlife a few years ago, we raised the alkalinity level dramatically by addition of a commercially available buffer. The next day, we noticed one of the broodstock corals (tentatively ID'd as Acropora millepora) had turned from brownish to brick red. This was the only coloration change noted in the 1,200 gallon system that contained ~2,000 corals.

I had a theory that the increase of bicarbonate (as a source of inorganic carbon for photosynthesis) may have 'turbo-charged' photosynthesis. However, recent experiments using a PAM fluorometer have not confirmed that this was the case. Exactly why the A. millepora demonstrated such a dramatic, overnight change in coloration is still a mystery.

For whatever reason, the addition of the buffer may have triggered the coral to expel zooxanthellae. This could more reasonably justify the sudden color change, rather than suggesting the reproduction of zooxanthellae. 'Destructive' biological processes like this may have been, often happen more rapidly than 'constructive' ones. I am saying that observations have shown that corals will 'bleach' faster than they will increase symbioant density.

Dana, were you also suggesting that the zooxanthellae multiplied in the absence of photic energy (overnight)?