Large water change BUUUUUUT. Not more than 50% that will cut it in half.
Depends on size of tank if you could do a 70-75% change.
3 ammonia is really high, and just weird for an established cycled tank even if abused a bit on food, the
bb should size up and deal with it and you should have
nitrites also that are high to show them working on it.
Sechem prime says it will bind ammonia and nitrites and make them non-toxic for 48 hours a dose, it works for me, but I don't know if it's myth or fact. I use prime myself and like it and I think it works.
Anyways the prime is supposed to make ammonia and nitrites and nitrats non-toxic for 48 hours.... up to 1ppm on the recommended dosages. About nitrites and
nitrates, it's antedotal, not scientific fact.
Double dosing prime is also antenatal to bind and detoxify more ammonia than 1ppm, it's not scientific fact.
A strategy that should work. 50% water change will reduce the ammonia to 1.5ppm.
A dose of prime will bind and detoxify 1ppm ammonia for 48 hours. You'll be left with .5 toxic ammonia. 50% water change tomorrow should remove .75 of the 1.5 ammonia that's left. And by the 48 hour mark you are redosing prime and ammonia is low again what's left is bound and detoxifies and back to regular water changes from there.
If nitrites are up also, 1 teaspoon (5 grams) of
aquarium salt per 20 gallons of tank water has been scientifically been shown to detoxify nitrites (Noga, 2010) just make sure you don't have any salt sensitive fish that can't take a bit of it.
The 50% change first though to cut the numbers in half, then treatment to buy some time to do another 50% then a 20% as normal.
Maybe he overfed some, but honestly it sounds like he did something else to crash your cycle, maybe changed out the water thinking it was dirty or something, due to the overfeeding... trying to fix the feeding mistake... maybe cleand out the filter in the sink and water change... just weird.
Also I don't like rapid successive large water changes without knowing more about the tanks parameters. If your cycle was crashed, you are stuck doing a
fish in cycle for a month and all those big water changes won't help with that to get it recovered, you'll still build ammonia and have nothing to convert it.