20ppm Nitrates

[whatcaneyedo]

What kind of filters do you have? If they are 'mechanical' filters like canisters and hang ons containing pads and sponges they are trapping and holding waste allowing it to break down and turn into nitrate. A protien skimmer essentially removes the waste before it breaks down. Either way they should be cleaned at least once a week or more for a saltwater system to keep them running efficiently and prevent nitrate buildup.

[RedCoralEdmonton]

Also how much live rock do you have? this will also play a part, even though the fish eat all the food given to them, they also poop...

Steve