I posted a few weeks ago about my algae problem, and the source of the problem now seems to be obvious. i did a water test today and my nitrates were through the roof. the ammonia and nitrite levels were fine at almost 0 ppm, and my ph was a little high (around 8.4). I feed my fish frozen foods (about 3 small cubes) once every other day, and i make sure all food is eaten. between those days i feed a small amount of flakes and some pellets. again all food is eaten. is there anyway to reduce my nitrate levels? i have a deep sandbed and i make water changes every week