Did you check the water you use for wc?
Is your tdo meter reading zero?
If you use tap water or even rodi water when tdo reading is more then 10
then you will have this type of problem
Cleaning crew or phos removal and nitrate removal all these are supporting
water to have clean pristine water.
It is still better to trackle your water source.
Ensure you are using tdo zero rodi or di water.