Whats causing my water propagated piece lily to rot?

A while ago, I had made a post about buying a piece lily to bury my pet fish. In the process of attempting to bury the fish, I had stressed out her roots alot and am inexperienced with house plants. I ended up burying him somewhere els and gave the plant away but kept a few pieces cuz I hate giving up.

I had her grow in water and she grew lots of new roots and in the process of grow more leaves (there was originally 3). Though, last two guys arent doing well. They where also growing but once again have root rot. Even the big one is starting to smell a bit. Is it an issue with them sitting in water?

How did I kill root rot last time? I cut off brown roots, brushed the rhizome, washed the pot, poured hydrogen peroxide onto the rhizome, and finally add her into her pot with Declorinated water only on the roots underneath the rhizome. I top it off with fish tank water.

Lighting? Window light and desk lamp with grow light 6-8 hours a day(not including window light).

Thank you!