I’ll address what I know. Testing water: if ammonia is high it can damage their gills. There are products you can get which will bind the ammonia so it won’t harm them, but it’s not a dose it and forget it kind of thing. Instead, you should consider how high it is, why it’s high, and address that. Ammonia is just step one of the nitrate cycle. We have threads on that which can explain it better than I can. Long story short, ammonia breaks down into nitrite( I think it’s that one) which is still pretty toxic to fish, then a different bacteria turns that into the other form ( nitrate?) which won’t be near as bad for the fish, but plants love that form, so having a pothos or peace Lilly in the hang on back filter will help remove that from the water. The thread on the nitrogen cycle can explain better than I can what steps should be taken when. If things are a little high for a short while, it shouldn’t harm the fish. But if it’s a lot high and isn’t changing for the better, things like water changes should be considered. As for training fish, my guppies know if we are washing dishes, they can con us into food. And my bettas know if they stare hard enough, I’ll feed them too. If you use the clicker every time, and toss out a bit of food, they’ll eventually hear the clicker and head your way. But it could also be that they see you and head you way with no clicker... they keep an eye on the edge surface of their pond for scary stuff. Same will go for the aquarium, they’ll be watching for scary stuff.
