How about you take a picture of what you are describing? What it sounds like is cyanobacteria. Cyano
is a sign of poor water quality and if in large enough amounts will lower the nitrate levels, providing a false reading.
water in water changes and top offs to prevent nitrates/phosphates from entering this way.
Lower the amount of food you are feeding, most fish do not need to eat everyday to the point where I only feed my reef tank every 3 days.
Increase flow, as cyano
thrives in low flow areas. But keep in mind, increasing flow will only mask the problem if the nitrate/phosphate levels are not addressed it will show back up as nuisance algae which is even more difficult to battle.