I have a 20g fish only/quarenteen tank with a fluval 304. 2 damsels, 1 trigger and a hermit. I spend most of my time on my reef tank, so I guess I may neglect this tank a little. I took a nitrate reading tonight and it was at around 25-30ppm. When will the trates start to be harmful to the fish?? I am trying to do as little maint. to this tank as possible. I have not touched the tank for at least a month until tonight. Dave