ammonia and no2??
IMO, washing of bio balls will wash away
the good bacteria causing ammonia
and no2 to go up. i think your fish
dia because of this..
wash bio balls after 6 - 8 mth to
prevent clog...only light wash as not
to wash away all the good bacteria.
50% of water change will make your fish
stress. try change 10% weekly and monitor
ammonia, no2, no3 before water change
( for a month)
..once water is mature can do 20% mthly
(depend on tank size and filteration system)
don't add in new fish...wait until water is stable
Get a good skimmer....
Most important thing....Patience