why is this a bad idea?

[mogurnda]

cichlid effluent for nitrate/phosphate?
I have been using plantbrain's recipe to supplement K/NO3/PO4/SO4 to my planted 25 tall, and am wondering about just adding KCl and MgSO4, and diluting water from my Tanganyikan tank for PO4 and NO3. It's probably just as easy to dump all the water from the cichlid tank on the azaleas, and the chemicals are cheap, but there's a certain appeal to using output from one tank as input to another.

[OrionGirl]

I would be concerned about the other dissolved solids/organics that would be piling up. Most should not be a problem, since most are protiens and will denature eventually, but they might impact any fish in the planted tank.

[mogurnda]

Given the relatively high levels of NO3/PO4 in the cichlid tank, it would only be about 10% of the input to the planted tank. So 90% of the input would still be from the tap, for better or worse.

[OrionGirl]

Up to you, but NIMT. I don't know the ratio for those dissolved solids causing harm, I don't know how high the concentration is in the effluent, much less in the planted tank. Without knowing these things, it's going to be very hard to prevent a problem, IMO.

[mogurnda]

I appreciate the input. I certainly posed this as a question to get feedback. As an aside, what compounds are you thinking about? Obviously, I want to get metabolites out of the cichlid tank, because they just increase the level of pollution, but it seems like the very same compounds would act as sources of N, P and C for the plants.

[OrionGirl]

Hormones are the first thing to come to mind--mostly protien, quick to break down, but will impact the fish in planted tank.

[mogurnda]

Not sure I'd worry about peptide hormones. It's likely they would be derivatized or broken down before excretion, and probably would not be absorbed by the fish in the plant tank. Interesting idea, though, and I should probably read more about hormone metabolism in fish.
Steroids seem like more of an issue, since they easily cross membranes. But even they would probably produce a small peak before being sopped up by plants and bacteria.

[OrionGirl]

Sorry--from my understanding, hormones are specific types of steroids. Many are excreted by the dominant fish in a system, and will stunt other fish in the same system. I don't know if they have the same impact across species lines (ie, from cichlids to tetras), but without knowing I would be hesitant to say that it wouldn't impact them.