Fairly new tank about 8 weeks and cycled. 100 litre. Water parameters are ok. 6.6 to 6.8 ph, 0 ammonia, 0 nitrate 0 nitrite. Temp is around 26 to 27 C. The pump is 550/Hr. My only fish is a pleco and his skin looks discolored. Almost dirty or sandy. I feed him algae wafers and sometimes cucumbers as treat once a week