magnesium question

[lrasser]

I've been slowly switching my system over an sps dominate setup. I recently also added a frag tang with about 20 sps frags. My specs are as follows:

150g (act water volume)
PH 8.2-8.3
Cal - 420
ALK - 9

I'm dosing 110ml of alk and cal daily using 2 part and levels stay very stable. I've noticed that I've been dosing about 300ml of mag per week to keep my level at 1350. I have great sps growth as well as a coraline outbreak. My question is whether I should continue to manually add mag or can I simply add it to my dosing pump. I guess I'm curious if mag usage is something that will slow down or remain this high and stay parallel to alk and cal. I was always under the impressions that mag levels dropped slowly. If I leave mine alone i'll drop from 1350 to 1200 in a week. Just looking for some advice from experience with sps. Trying to make the transition to SPS a good experience.

 

[Boomer]

There is something very, very wrong there.

1350 - 1200 = 150 ppm / week

150 / 7 = 21.5 ppm / day. Can't happen. You can not get that in SPS dominated take with Calcium. You would have to have more corlaline algae then water, even then don't see it.

There must be some kind of testing error. How are you testing it ?

 

[lrasser]

i'm testing correctly and this has been for about two months now. From what i've been reading this isnt too out of the normal for some tank. I found this thread which helped shed some light on it. The system is just past a year since I moved so I've been getting a lot of sps and coraline growth. From what i understand this will settle down once everything settles in but I'll have to wait and see


http://www.reefcentral.com/forums/showthread.php?t=1852904&page=2

 

[jvu61]

i just dose it through my bubble mag I have a 300 gal and dose about 20 ml per day

 

[Nandez13]

What test kits are you using?

 

[lrasser]

I'm using the red sea kit. The reading are correct. I've double checked them against another. The trend drifts the same each time. From what i've read the substrate and live rock will soak up a lot of mag then eventually the consumption will slow down. I'm going to add it to my doser today but at a slightly lower volume then needed. This should allow me to keep it more stable but make less of a change I overshoot if it slows down.

 

[Boomer]

Irasser

Ok, you may get that in a fairly new tank and more so with allot of coralline.

Allot of fresh carbonate LR and sand/ gravel could do that. along with coralline. Fresh new carbonate surfaces have a affinity for Magnesium. This causes the carbonate surfaces to have overgrowth precip's we call High Magnesium Calcite. These prepcips can deplete the Ca++, Mg++ and Alk allot in the beginning. This will all stop in time and get back to more normal dosing. With that said, what you and some are seeing is by far not a norm. The type of substrate, what it is, its grain size, the pH of the area, temp, porosity and total surface area are pretty much what controls it. Meaning, the higer the pH in that bed, higher temp, more surface area and porosity are what controls it until the surface of the material gets coated either from the High Magnesium Calcite, reaching equalibrium and or organic coatings which pretty much halts the process. And to add it is not just Magnesium, as Mg++ can not just leave by its self, it is taking Ca++ and Alk with it.

 

[lrasser]

Thanks Boomer. Thats right in line with all the research I've been doing.

 

[Boomer]

I kinda spaced that out, it is one of my pet subjects I actually have books with sections on this but only one aquarium related wrote 35 years ago. I must have been sleeping....lol

To add, Aragonite surfaces such as crushed coral are the worst, and the least is Dolomite, followed by Puka shells, with things like oyster shells in the middle. And the worst of all, if one could find it, would be very porous Calcite.

I do not know if you have heard of " cemented sand beds" in the reef tank but it is the same. If the sand is to fine and this takes place your bottom turns to cement, "glueing" the grains together and you need a hammer to break it up. In carbonate petrology we call this Early Marine Diagenesis. And if you use a lot of Kalk it is more apt to happen, as it pulls out the CO2, raising local pH in the SB making precip more prone.

 

[lrasser]

I Have another tank that had that issue after being setup for several years. This is a 125 running 80lbs of Fiji pink and about 160lbs of live rock. I've added 3 fighting conchs and other sand dwellers to keep the sand more stirred up. I've set it to dose 50ml a day and I religiously test alk, cal and mag at LEAST once a week. I'm going to maintain it at 1300 so even if the substrate completely stops absorbing the mag it wouldn't go any higher then 1400 with the additional dose for that week. With the current consumption levels I feel this will keep them the most stable which is most important. I'm trying to avoid and fluctuations.