Advanced Water Chemistry Question

[AquaBear]

Hello forum....

I have what I think is an advanced water chemistry question. Maybe it isn't that tough, but it's way over MY head.

I have a 75g FOWLR tank with 80 lbs of LR and 55 pounds of crushed Florida coral for a substrate. This tank has been established for almost a year now, and the readings are pretty good. Ammonia and Nitrites are zero, Nitrates are less than 10, pH is 8.2, phosphates are 1.0, SG is 1.023, kH is 9, calcium is 340, temp is 78. This tank is pretty stable.

Sitting right next to it is a 35g refugium that I am building. It contains 60 pounds of LS (40 of Nature's Ocean Bio-Active Aragonite Reef Sand and 20 of CaribSea Arag-Alive Aragonite Reef Sand, if that makes a difference) and sitting on top of that is 22 lbs of freshly-cured LR. Ammonia/Nitrites are 0, Nitrates are 5, SG is 1.023, no phosphates (it's not stocked yet), pH is 8.2 but tends to drop, kH ranges from 11 to 14, and calcium is also 340.

The fuge is not yet spliced into the main tank, because my pH and kH are still fluctuating. The pH has dropped as low as 7.8 and I've added Sea Chem's pH-raising product, which fixes the problem, but only temporarily, then it starts to fall slightly. I intend to house detritivores (snails, crabs, sea cucumber, sand-sifting star and whatever else makes sense) in the fuge, as well as cultivate pods and perhaps grow some algae for the final stage of nitrification, all of which is to benefit the main tank.

My question is, what can I expect to happen when I splice the fuge into the main tank's sump? Can I expect that the stability of the main tank will carry over into the fuge (remember, it's just over half the total volume of the main tank), or will the unstable pH problems in the fuge start causing my main tank to have pH/kH problems? And if it does, do I treat the water in the main tank, or the water in the fuge? How should I treat it? Boost the pH/kH only, try to increase calcium or.....?

I've put a lot of time and money having a custom fuge built to help the main tank, and at the same time make the fuge a showpiece in it's own right (the intent is to make it look like a little reef tank, but with no coral or fish). The LAST thing I want to do is screw up the chemistry in the main tank and cause the bio-filter to crash. I've never really paid attention to the kH and calcium before this, so I'm a little confused on what to do next.

Any suggestions would be appreciated. TIA,

--Aquabear

 

[clowninround]

I am doing the same thing, and you are asking some good questions that I am also interested to know. However I do know if you run the lights on your fuge opposite of that of your tank it will actually make the ph more stable. It won't lower at night because the lights are always on somewhere in the set up. I don't think switching it over will cause any ill affects, if it does than I am in for trouble also. Here's what I am thinking though, when u put in the fuge, you add water volume (at least I will be, 25g), this is going to help stabalize your water parameters. I don't think adding water is going to screw up the chemistry unless you are using a different salt or something. If I am wrong, please someone correct me. Also if you are treating your tank with seachem ph stabilizer it is better to put it in your sump or fuge so that it spreads around the tank evenly. You won't need to dose seperately.

 

[JG]

I'll take a stab at it. Aragonote and your crushed coral are both the same chemically, however the structure of the molecules are different and their solubilites are different as well. Aragonite that forms as an ocean sediment has more Magnesium in it and this changes its ability to dissolve in water.

My guess is that your crushed coral is dissolving more readily when the pH gets lower and thereore is bringing the pH back up. The crushed aragonite is a bit slower to dissolve and so your pH fluctuates.

Joanne

 

[sevise]

I recently upgraded my sump/fuge from a 30gal split into sections to a 100Gal stock tank(filled to about 80Gal) and a 30Gal Fuge. My display is a 120. I set them up and just let it run. I figured it was basically a 50% water change. At the time all I had was a school of Chromis so if something did go wrong I wasn't going to loose tons of $ if the livestock died. It may be different for you.

Up until last week I had always lit my fuge 24/7 , however after setting up my aquacontroller and seeing the pH drop at night I decided to try reverse lighting. I went from a 0.1 nightly drop to a 0.6 drop. Currently I light the fuge exactly opposite, I'm thinking of experiementing with starting it earlier so the macros have time to ramp up there O2 production before the main shuts off. However thats on the back burner until I get my Ca up to acceptable levels.

 

[JG]

Now that it is not so early in the morning and I have finished my coffee ..... I have a few more chemistry thoughts.

Thought #1 Coral and Aragonite are both calcium carbonate molecules. The coral is suposed to dissolve more slowly in the water. Pure aragonite should dissolve more quickly than the coral and act as a natural buffer. However, the aragonite taken from marine sediments has a lot of magnesium tagging along. This makes the aragonite dissolve more slowly.

Thought #2 Temperature will affect both. The higher the water temperature, the faster they will dissolve.

Thought #3 Surface area will affect both. The activity takes place on the surfaces of the particles only. The finer the grain, the more rapidly the carbonates are dissolved. If the aragonite is coarse - smaller overall surface area of your substrate - slower dissolving - less buffering effect.

Thought #4 bacteria, and animals give off CO2. Co2 and water forms Carbonic Acid. Carbonic Acid drives pH down. Lower pH dissolves more carbonate. Perhaps as you establish more critters pH will stabilize.

Thought #5 Probably a combination of #1, 2, 3, and 4. Nothing can really be simple.

 

[AquaBear]

WOW. What was in that COFFEE??!!

Thank you ALL for the information. I've read it, it makes sense and I understood pretty much all of it, so I appreciate the explanations. (I'm a technical person, so I just HAVE to know WHY) I'm going to do a water change tomorrow with about 5 gallons of water from the main tank, to start introducing more of the bacteria from the tank it will be connecting to. And I will continue to monitor the pH/kH to understand how the cycles fluctuate.

I use only Instant Ocean for all my SW tanks, and I keep them all at pretty much the same settings. I forgot about the water volume thing, but that's a very good point. I believe I will run it on reverse cycle from the main, which gives the benefit (?) of having light bleed into the main at night to simulate full, bright moonlight. I could put up cardboard to cut that back if it becomes a problem for the nocturnal fish.

At this point, I'm definitely planning on macro-algae (Caulerpa and maybe Sea Grass...any other suggestions?) and leaning heavily toward a Sifting Star and Sea Cucumber to help sift the sand. 60 lbs in this square footage equates to about 3 inches of sand, and I don't want to risk developing anoxic/anaerobic areas. Plus some Nassarius and/or Conch snails. I'd love to keep a few Emerald crabs in there, but I've mixed crabs w/starfish before to deadly results for the star, so nothing with pincers. But there's no sense adding livestock yet if there's nothing for them to eat. And leaving the light on without stirring it was turning the LS brown.

A guy at my LFS suggested adding Kent Coral Builder to help raise the calcium and/or kH. I guess I need to do some research on the very special needs of this kind of setup. Can anyone offer a Cliff's notes version of, or point me to a site/post that explains how things like magnesium, strontium, calcium blah-blah-blah are supposed to work in VERY simple terms. (I failed high school chemistry, after all).

Many thanks again to all of you for the kind advice. It's nice to know there are others out there who also think on this scale. I'd be interested in hearing why any of you specifically added a fuge to your setup and if you really think it makes a positive difference.

--Aquabear