If the discus has bright red eyes and and it changed to dull red towards black. Does this means there is an health issue coming up?
Usually an indication of a toxin build up Jim, even prolonged exposure to nitrite can cause it,
Do a polyfilter test,
thanks, will do a poly test later.....How long does it normally take the discus to flush it out of their system?
Depends what the cause is Jim, nitrite within hours, metals can take a few days depending on the health of the fish...................