Just wanted to thank everyone here for your help and support while my betta was sick. He had fin rot but it seems to be healing now. While I was gone on vacation, I asked my coworker to feed him and give him more treatment if he looks worse. He has been back in the 3 gallon tank and is doing fabulous! His color is back and the fin looks like it's starting to grow back.
The weird moldy thing is starting to accumulate again in both tanks I have and I think I just have to live with cleaning it all the time. i dont' know what I'm doing wrong but it looks like it's gonna be fine as long as I clean them. I checked the water and it's fine.