Alk, Ca, Mg and Fish

[yort265]

I know the importance and role of the reef foundation elements Alk, Ca, & Mg when it comes to coral. I also know that when it comes to these elements, that stability is more important than being dead on accurate...BUT when it comes to a tank that currently has no coral and just a couple if hardy fish, how important are they? how fast can they be changed/dosed? thanks. Troy

[blanden.adam]

They are important because they all exist in an interrelated balance, and Alk is what gives your tank pH stability (important for fish, but not as much as for corals), but they don't have to be as tightly controlled. BUT, i would stick to general rules of thumb about changing them slowly because if you change them to fast you can end up with abiotic precipitation of calcium carbonate.

[Denbf58]

doing fish only regular water changes should keep it stable

[Sk8r]

Here's the deal: fish get uncomfortable when alk goes off. Alk is held stable by the ratio of calcium and magnesium in the water. Fish use calcium and magnesium: calcium produces bones and drives muscle movement and keeps the heart beating, and magnesium helps regulate chemical processes in their gut, etc. But what they use is miniscule compared to corals' draw on both. Therefore most of these elements can be supplied by your regular water changes.

The key is testing alk, for a fish-only. Ph is pretty irrelevant for a marine tank, because it shifts throughout the day; if you start trying to adjust that, you're likely to screw your water balance. Test alk, which bears a relationship to ph, and you'll know what's going on. If you find your alk continually dropping, continually needing you to intervene, your water balance is shot and shot so thoroughly that your water changes aren't keeping up with it.

How to fix? Step one is to test the magnesium and get it to 1300.
Step two is to bring the alk to 8.3
Step three is to bring the calcium to 420.
Then it will stay steady, helped along by your water changes, until your fish have gradually pulled enough magnesium out of the water to destabilize it again. The destabilization doesn't happen for a long time in a fish-only tank, because the draw is so small. One little clam or stony coral can zap the stability in short order because of their appetite for calcium and magnesium: people who have either stony coral or a clam need to supply calcium on a daily basis, the same as you actively feed your fish. But remember fish drink with every breath, so they are using the content of the water as part of their diet, and they need to have that calcium and magnesium available to them, as little as they do use.
HTH.

[dotcommer]

Originally Posted by Sk8r

Here's the deal: fish get uncomfortable when alk goes off. Alk is held stable by the ratio of calcium and magnesium in the water. Fish use calcium and magnesium: calcium produces bones and drives muscle movement and keeps the heart beating, and magnesium helps regulate chemical processes in their gut, etc. But what they use is miniscule compared to corals' draw on both. Therefore most of these elements can be supplied by your regular water changes.

The key is testing alk, for a fish-only. Ph is pretty irrelevant for a marine tank, because it shifts throughout the day; if you start trying to adjust that, you're likely to screw your water balance. Test alk, which bears a relationship to ph, and you'll know what's going on. If you find your alk continually dropping, continually needing you to intervene, your water balance is shot and shot so thoroughly that your water changes aren't keeping up with it.


How to fix? Step one is to test the magnesium and get it to 1300.
Step two is to bring the alk to 8.3
Step three is to bring the calcium to 420.
Then it will stay steady, helped along by your water changes, until your fish have gradually pulled enough magnesium out of the water to destabilize it again. The destabilization doesn't happen for a long time in a fish-only tank, because the draw is so small. One little clam or stony coral can zap the stability in short order because of their appetite for calcium and magnesium: people who have either stony coral or a clam need to supply calcium on a daily basis, the same as you actively feed your fish. But remember fish drink with every breath, so they are using the content of the water as part of their diet, and they need to have that calcium and magnesium available to them, as little as they do use.
HTH.

Very Well Put

[yort265]

thanks for the responses. my tests show the following: alk - 8.1; cal - 430; mg - 1400. seems like everything is in balance. I'm currently testing alk every 24 hours to see how much the tank is using, and it looks like about .5 dKH a day. the only big alk consumer I have in the tank would be a piece of live rock I got from a friend that was encrusted with coralline algae. does this seem about right? the only other inhabitants are a pair of tank bred false percs. they seem happy, but have no home so they stay in a corner most of the time. I was trying to get water parameters stable before getting a couple of pieces of coral... I want a torch to see if it'll host the clowns. thanks.

[cvsailer]

Originally Posted by Sk8r

Here's the deal: fish get uncomfortable when alk goes off. Alk is held stable by the ratio of calcium and magnesium in the water. Fish use calcium and magnesium: calcium produces bones and drives muscle movement and keeps the heart beating, and magnesium helps regulate chemical processes in their gut, etc. But what they use is miniscule compared to corals' draw on both. Therefore most of these elements can be supplied by your regular water changes.

The key is testing alk, for a fish-only. Ph is pretty irrelevant for a marine tank, because it shifts throughout the day; if you start trying to adjust that, you're likely to screw your water balance. Test alk, which bears a relationship to ph, and you'll know what's going on. If you find your alk continually dropping, continually needing you to intervene, your water balance is shot and shot so thoroughly that your water changes aren't keeping up with it.

How to fix? Step one is to test the magnesium and get it to 1300.
Step two is to bring the alk to 8.3
Step three is to bring the calcium to 420.
Then it will stay steady, helped along by your water changes, until your fish have gradually pulled enough magnesium out of the water to destabilize it again. The destabilization doesn't happen for a long time in a fish-only tank, because the draw is so small. One little clam or stony coral can zap the stability in short order because of their appetite for calcium and magnesium: people who have either stony coral or a clam need to supply calcium on a daily basis, the same as you actively feed your fish. But remember fish drink with every breath, so they are using the content of the water as part of their diet, and they need to have that calcium and magnesium available to them, as little as they do use.
HTH.

Great summary. If your alk is 8.3 is it safe to assume that your calcium and magnesium are in safe ranges?

[blanden.adam]

Originally Posted by cvsailer

Great summary. If your alk is 8.3 is it safe to assume that your calcium and magnesium are in safe ranges?

You can't really make that generalization. The only way to know is to test. The only case that I know of where this might not be precisely accurate is in a reef aquarium when trying to "dial in" dosing of calcium and alkalinity with a balanced additive. Alkalinity will vary much faster than calcium, so you tend to test alkalinity more often, and because they are consumed in a defined ratio, you can be pretty certain of your calcium level. However, even this drifts over time. In short, you just have to test to know. But in a FOWLR because they change so slowly, frequent testing is not a necessity as it is in a reef.

[Sk8r]

Once you know your tank, you can use your alkalinity as the 'bellwether' reading to predict the others, but a mg test can be just as good. Alk is the easiest Salifert test to run, so that's my usual recourse.