mechanical media (filter pads, and bio balls) can be hosts for nitrate factories. However, depending on what all you have in your tank will also play a roll in amount of nitrates. The rule that i go by is 'if you have at least 1 pound of live rock for every 1 gallon of water, then bio balls are going to create nitrates'
also, it is important to keep your filters clean...I usualy rinse my mechanical filters under tap water about once or twice every 2 weeks....
other factors include....what type of water do you use? (tap, RO?)
tap water can have trace elements that promote unwanted algae growth and nitrates.
also if you are using Amquel to treat your water, this may have a ill effect on your water test results....
I too had this nitrate problem not too long ago so some of the steps i took were: removed bioballs (progressionally), stoped using tap water (used water from walmart .33/gal) and stoped using amquel...
hope this helps!!!:yes: