the idea was to mix the fluorescent substrate with the stuff that's in there right now; that way, it shouldn't glow throughout its depth, since there's other sand in there that would absorb the light. my main concern is whether the stuff would be toxic. i mean, its being sold as substrate, so i suppose its relatively safe, but how safe is relatively safe? as far as the light is concerned, i wouldn't put it right on top of the tank, so i dont think it would do any harm. any takers?