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monkeysea

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Hi,

I'd like to get some feedback on my design for an almost maintenance-free pico. I have this design set up right now in my office and it seems to work.

The design is basically a gravity-driven system where clean saltwater siphons down at a controlled drip rate into the main tank. From the main tank, when the incoming water pushes the waterline above the overflow, the overflow siphon draws the excess water out into the cup, which has a bulkhead and a drain tube leading to a bucket on the floor. So, all I have to do is keep the top container filled with water, and clean water will constantly flow in, and dirty water (mixed with clean water, of course) will automatically flow out the overflow and into the bucket. In other words, this is a simple continuous water-change system.

The top container is 2 liters, as is the main tank.

I hope to be able to leave this system running days at a time with the only maintenance being filling up the top container and emptying out the bottom bucket. Periodically I will check to make sure that the top clean saltwater container is draining and that the drain bucket is filling up, which indicates that water is correctly flowing through and being changed from the main tank.

There is no fresh-water top off. A lid (saran wrap, currently) slows evaporation. Drip rate of the incoming clean saltwater line must be faster than the evaporation rate (otherwise the waterline would never rise above the overflow and no water would ever leave the system). I plan to control salinity by periodic measurements of the main tank's salinity and corresponding adjustments of the salinity of the incoming clean saltwater.

Now, as I said, I have this set up experimentally (no livestock yet) and it seems to work fine. However, I'm still a little afraid of leaving the system running unattended and coming home to water on the floor.

In particular, the overflow line (an airline tube acting as a siphon) is a single point of failure. In the event that this tube loses its siphon, then incoming water would overflow the main tank and spill on the floor. Specifically my overflow is a small vial inside the main tank with a corresponding small vial outside the tank but slightly lower, with a siphon tube connecting the two. Ordinarily there will always be water inside both vials so it should be "impossible" for the siphon to ever lose its suction - unless the tank or the overflow is bumped so severely that air is allowed to enter the siphon tube.

So, what I'd like to ask is - how can I prevent or make contingency plans for failure of the overflow siphon? Also, are there any other flaws or weaknesses in this design?

Thanks for any feedback. I really hope that with this automated system I can again enjoy small-scale reef-keeping. My previous nano ran for a year before it crashed due to neglect. I hope that an automatic continuous-flow water change system will allow me to take proper care of my system.
 

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Anonymous

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your drip rate might be faster than the evaporation rate, however you will still get some level of evaporation.
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ChrisRD

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Hi and :welcome:

I've heard talk of the continous drip / water change thing before, but I can't say I've ever seen anyone implement it. Seems like a good idea...

Two things I would do differently to eliminate possible problems. For one, I would feed the incoming water to the display tank with a dosing pump to ensure a consistent drip rate. It wouldn't have to be fancy - an inexpensive single channel pump controlled by an appliance timer would work fine.

Another thing I would do is drill the display tank so it could gravity drain to the last container. I wouldn't trust a syphon, especially at very low flow rates, to remain reliable over time.

JMO & good luck with your project! :)
 
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Anonymous

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Yup, you need a more reliable siphon, maybe considering using the AquaLifer or similar pump if you can't drill the display tank for a overflow.

Knot is not reliable, since it can get clogged or unkinked. Use one of the plastic needle valve maybe better, or as Chris mentioned, use a dosing pump.

Continuous drip/water change is not efficient since it waste a lot of salt and water. This is why it only implemented in small number of cases. But for nano, the water volumn is small enough that this economical issue can be overlooked. :)
 

SnowManSnow

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I would be concerned about salinity levels. With continuous evaporation and the constant addition of new salt water.. whouldnt your salinity slowly rise?

There seems to be a balance issue to me.. just not sure how to explain it.
 
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Anonymous

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The new salt water need to have a lower salinity than the display tank water. The difference is determined by the drip rate and evaporation rate.
 

monkeysea

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Thanks for the helpful feedback. A couple of extra comments...

First of all, I'd prefer not to drill the tank: I don't have a drill, and my previous attempts to forcefully tear holes with crude pointed instruments generally led to cracked plastic. After recently understanding the wonderful concept of the "overflow box", I realized that it is possible to drain the main tank without drilling it.

Second of all, another design parameter was to keep this electricity-free. Call me a purist, but I wanted to see if a mostly-automated water change system could be achieved just with gravity and without using electricity or pumps to move water around.

I agree that a valve would be a better way of controlling the incoming drip rate. I'll look for one at the LFS.

Using a valve for the incoming drip also somewhat alleviates my concerns about overflowing the main tank with water ending up on the floor. In order for the water to end up on the floor, TWO pieces of the system would have to fail simultaneously: (1) the incoming valve must catastrophically fail, sending all incoming water flooding into the main tank, and (2) the overflow siphon must fail, not draining the excess water and overflowing the main tank. Both failures occurring simultaneously is unlikely, especially with daily inspection, so I'm somewhat relieved.

When I'm on vacation I'll just put the entire tiny tank (it's just 2 liters) inside a large plastic tub so that even if the main tank overflows, it will overflow into the tub and not the floor. Looks ugly, but on vacation, who cares?

I think my daily/weekly routine maintenance will be as follows:

Daily: visually verify that incoming water is dripping slowly into the tank, verify that main tank water level is not falling (if it is, evaporation is faster than drip rate), verify that main tank water level is not rising above overflow (if it is, overflow is blocked/siphon lost), verify that overflow siphon is filled with water, verify that some water has been drained into the waste bucket.

These daily inspections should allow me to catch any possible problems before they end up spilling water on the floor.

Weekly: check salinity level of tank. Refill incoming reservoir with new saltwater of appropriate salinity. Empty waste bucket.

Importantly, this maintenance regimen doesn't require me to stick my hands in the display tank every day, but still ensures a continuous (though of course diluted/somewhat inefficient) water change.

Can't wait to get some livestock :)
 
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Anonymous

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Sounds good. I used Lee's plastic needle valve (greenish blue ones, $2?) for air tubing, but never for long term. You may want to get some nice hard plastic needle valve (I think Petco is selling a gang air valve with nice clear plastic (can see if the thing get clogged) and black needle. Pretty cheap ($5?). Good luck.
 
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Anonymous

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FWIW here is one of my designs for a simple pvc hob overflow:

20060522overflow.jpg



Your salinity in the tank will be higher then the salinity of the water being added.

The tank will settle down to (the daily change)/(fraction of daily change)+ whatever is in the replacement water.

For instance, if you are increasing 2 ppm nitrate per day, using 30ppm nitrate replacement water and changing 1% of the water/day:


final nitrates= (2ppm)/(1/100)+30ppm=200ppm+30=230ppm nitrates.

or if you are changing 10%/day:

final nitrates= (2ppm)/(1/10)+30=20+30=50ppm

If course if the tank is fully consuming the nitrates then nitrates will be 0 regardless of the amount of water being changed.


.02
 
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Anonymous

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Does the formula work for a continuous water chang situation.
 
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Anonymous

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dupaboy1992":2xoj2boo said:
Does the formula work for a continuous water chang situation.

yep.

it actually works for the parameters before a water change.

But consider where the amount of water changes and time between changes are related. Say 1%/day and the magnitude of the change is tied to that. so 2%/2days, 10% 10 days and so on.

%_change_____days____just before change:

1/3____________33_1/3______3 times 33 1/3 day increase (100 times daily)
1/4____________25______4 times 25 day increase (100 times daily)
1/5____________20______5 times 20 day increase (100 times daily)
1/10___________10_____10 times 10 day increase (100 times daily)
1/100___________1_____100 times 1 day increase (100 times daily)
1/200__________1/2____200 times 1/2 day increase(100 times daily)

so in the limiting case a 1% continuous change results in a constant 100 times the daily production/consumption.




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