Hello everyone I have a 75 gallon brackish tank with a salinity of about 1.010. My ammonia and nitrite are 0 ppm. and I believe my nitrate is high looks like 80 ppm. I have an fx4 and a penguin biowheel 350 and an under gravel filter. I have 3 freshwater lion fish and one freshwater moray eel. Some of my freshwater lion fish have this white like patch ill attach a photo I have no idea what it could be and I was wondering if I should just remove the under gravel filter completely because I believe that to be the reason I am having high nitrates. I really love my fish and don't want any to die and would appreciate any help you can give me. you can see it on his tail fin and on the top fins on the right its like a white patch like thing I honestly have no idea what is wrong.