Welcome to RS.
I don't see anything specific that might be wrong. What do you see that makes you think there might be a problem?
Could you tell us more about your system?
How long has it been set up?
How long have you had the zoa?
What are your water parameters? Please post exact readings for these. Statements like "all parameters are fine" do not tell us anything. What seems fine to you might indicate a major problem to someone else.