What kind of chemicals do you put in it?
I dose B-Ionic 10cc of each part every other day.
I run a bag of ESV carbon in my aquaclear 24/7/365 and change it every 3 weeks when I do a 15% water change.
The best thing I did is add a 10 gallon refugium w/ colerpa algae in it. Since I set that up, I have not had to run a phosphate absorbant and my nitrates have not risen above 5ppm.
Not a chemical, but I also feed the corals D.T.'s every other day and some Marine Cuisine once every 10 days.