Sueet

I'm curious what about them, specifically, made you quit? And are you thinking they were still existing in your empty aquarium for a year? Highly unlikely unless you never cleaned it out before you set it back up. They probably came in on your plants. I love having detritus worms and copepods in my tank. If their population is what made you crazy, it's all about you overfeeding. If you stop overfeeding, their numbers will stay small/er.

Your picture is not clear enough for a positive id. Planaria have a very distinctly triangular head, if the head is rounded it is some other kind of worm.

An established tank CAN handle dying leaves. The problem is likely just the bba treatment, if you have to do it again, just be aware that everything that you kill in there will rot until/unless you clean it out. Even if you can't see the rotting particles, if you KNOW you killed things, do extra water changes, and/or add extra beneficial bacteria to help clean up the mess while the prime keeps it from being toxic. (prime wears off after a couple days btw, if you have a lot of ammonia in there, and not much bacterial/plant presence to pick up what gets released, you have a problem still)

Just wanted to mention if you mix cherry shrimp colors you will end up with a lot of brown/wild type babies.

Put food inside of a net and snatch it out when you have enough.

Chloramines are being used in many municipal water operations now, and that can give ammonia readings. Are you using any kind of water conditioner for water changes? I would recommend Seachem's Prime, but the api water conditioner works as well. Any time you treat for something like blackbeard algae, you are essentially filling your water with dead things that go on to rot - Even if they are tiny individual algae cells, that will also cause ammonia.