Hi, I have a 6 inch oscar and 8 4 inch silver dollars and 1 3 inch Convict in my 100g tank. The ammonia and nitrite readings are always 0 but my nitrates are usually 40-80. Should I just do more water changes or is the tank overstocked and I should get rid of the silver dollars? I do 25% WC every week or week and a half, Im out of town a lot. Thanks for any advice.