Not trying to flame or anything, but just a suggestion, make sure your test kit is reading accurately.
I had an API nitrate test kit go bad and didn't even realize it for awhile because I just wasn't really thinking about it at first. Then I realized my overstocked 125g, which had previously tested around 40ppm most of the time before water changes, had tested at 10ppm several times in a row.
Well, I used the kit on my turtle tank and sure enough it read 10ppm on that also. NO WAY. My turtles produce WAY too much waste to have nitrates that low even if I was doing water changes every day.
Went and bought another test kit, and the tank was actually testing about 20 ppm, that's after I'd done a 50% water change.
So yeah. If you're getting constant 10ppm readings, especially if you're using API, please make sure to verify your results for the sake of your fish.