Thanks, BigC. I think the water disturbance is the problem, because I keep the 50 gallon tank (where nothing survives) in a double stand with a 35 gallon tank in the bottom, both natural light, and both injected with CO2 and fertilizers, pretty much the same treatment, conditions and biological load, yet the plants in the 35 thrive, though it gets less light, being the bottom tank. The 35 has air-driven filters, with flow rate at low--plants are potted, not planted into gravel. I'd like to convert the 50 gal to full planted soon, though...