Jerry and Alani, Alani's setup sounds different in a few ways from yours. Alani can correct me if I'm wrong, but it sounds his tank is both long-established and holds fish as well. Whatever may have been the starting material, his substrate likely contains substantially more material than the fine gravel he started with. His fish are presumably fed fish food which directly or via the fishes' digestive systems becomes fertilizer (both liquid and solid) for the plants in the tank. Ive seen permaculture systems that use a tank full of (regularly fed) fish to provide dissolved nutrients to a hydroponic bed of salad greens. Considering a major component of both fish food and fish emulsion (a plant fertilizer) are fish meal, it doesn't seem surprising that additional fertilizers aren't required when you also keep fish in a tank. Animals are both wasteful and profligant in their use of nutrients. Fish, in much the same was as cows, act as living fertilizer factories for the plants around them. Since you you don't have fish, however, you're going to need some source of additional nutrients besides the gravel or rockwool in which your crinums currently grow. -|<ipp