"Regular" ferts in my tank?

[lectraplayer]

Has anyone thought about "regular" fertilizers in their tanks with or without fish? I am cycling a planted tank (fishless) and have wondered about a 20-20-20 mix I have for my house plants. I see stuff like ammonium nitrate and a urea compound, and my first thought there is both turns to ammonia, but has anybody given thoughts to agriculturally-oriented ferts in low doses for starting or maintaining planted tanks? What all is normally expected to be toxic to fish and does it cycle away?

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[Old Scales]

Land plant fertilizers are based on ammonium nitrate and urea which are both toxic to fish. If you'll note the nitrates for aquatic plants are based on potassium nitrate which is not. This is an age old proposal done and regretted by many. OS.

 

[lectraplayer]

I figured something would nuke my fish if I used land-based ferts. Is the main reason for the toxicity an ensuing ammonia spike as the ammonium nitrate and urea breaks down? Are there any other hazards?

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[Old Scales]

Most of the time the land based ferts are too acidic for fish also. Adding it to the water in a tank can knock down pH too quickly for fish. About the Urea. Think Uric acid. OS.

 

[lectraplayer]

That's what I was thinking. Urea (uric acid aka "P") becomes ammonia, nitrites and nitrates. All cycles to nitrates in a healthy habitat, right? Problems occur when the biofilter is not up to the challenge.

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[lectraplayer]

I will have to do some titration tests to check on what to do about the PH. Sodium bicarbonate will likely be involved if I go beyond the lab, unless I can supply potassium and/or phosphorous with my alkaline buffer.

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[Mebbid]

For about $15 you can get a combo pack of all the ferts you need for an aquarium without any of the issues of land based ferts. It should last a normal person a year or more at that rate as well.

Aside from the obvious ammonia and ph issues I can't even begin to imagine how imbalanced the fert ratios would be in a terrestrial fertilizer when compared to the specifically mixed amounts we use. Aquariums can be delicate, its just not worth it to save a few bucks if you accidentally nuke your tank with a mismeasured dose.