I've always wondered what would happen if dead plants and fecal matter lay in chlorinated waters and/or waters treated with strong antibacterials or antibiotics.

I've heard that aquarium tanks owners warn against using strong antibiotics as it can kill nitrifying bacteria which convert toxic ammonia to a safer form of nitrate. Otherwise, ammonia levels can buildup and be toxic to the aquatic life in the tank.

However, that doesn't make sense to me. Even if the nitrifying bacteria die, wouldn't the ammonifying bacteria which produce ammonia in the first place also die? Would there be greater amounts of ammonia in the water after these agents are repeatedly used, or would ammonia levels with nitrate levels together fall significantly?

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    – tyersome
    Commented Jun 15, 2020 at 22:36

1 Answer 1


A very large part of the bacteria and fungi will die so very few biological processes will continue in the tank if you add chlorine or antibacterial chemicals.

Ammonia will slowly outgas from the water oxygen and CO2 will reach equilibrium in the water as little oxygen is used and little CO2 is produced, it is the same with the other atmospheric gasses.

Life in the tank will simply stop until the toxins are broken down or removed,by toxins i mean chlorine and/or antibacterial chemicals.

Nitrate level will not change as little is produced and little is used, any denitrification will stop too.

Denitrification can only happen in an anaerobic environment but denitrfying bacteria too are killed by chlorine and antibacterial chemicals.


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