No one else has said it.......So I have too........The conditions in that laundry tub you are using is appalling. Its a miracle any of them are still alive.
YOU NEED A BIGGER TANK!!!!!!!!!!!! You can stuff all the biological media in that tub you want and it wont help. You need water volume man.
I know its expensive, But its time to get a big tank and more filtration or they will slowly die off.
Slow down on feeding and do 2-3 25% water changes this week

and try to improve your water quality before you kill your fish