Does it eventually become exhausted, even to the point where root tabs cannot bring it back? I am trying to figure out why my tank has turned into a disaster area after years of healthy growth. I have 20 ppm N03, 1.0 ppm Fe from traces, 2.0ppm PSO4, and a green drop check during most of the 55 watt photoperiod over my 29 gal tall. It's the only possibility I haven't considered after months of frustration. I recall that when I first started out 12 years ago with Aquasoil and DIY C02, the tank looked fantastic no matter what I did.