My fish have torn fins.

I'm jumping in way late, but...I think you found the main cause of frayed fins, the krib & low ammonia level.. In old houses with shallow wells there can be run-off issues, usually "just" high nitrate. Prime is a very good dechlor but also a way to keep ammonia in the safer "ammonium" form, NH4+...it still shows up as ammonia with API type tests as the more harmful NH3 & also high nitrates. I'm glad you got your job back, my husband is out of work ATM too...luckily I had invested in a gallon of Prime, lol. Water changes of 30% or more should always be safe unless your water company (not applicable to you) goes crazy with "seasonal treatment" or you have a hurricane or similar catastrophic event...& those can happen...
 
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