Hi, The nitrate level in my 55 gal is very high (the test reads 50). How should I bring it down? I already did a 10 gal water change that didn't make much difference. How often should I change my water to bring it down? I saw an additive at the fish store that says it removes nitrates, you guys think it's a good idea to use that stuff? I also have a hang on power filter with no media in it, I just use it for more water movement.....could this be what is causing the high level of nitrates?