I do not believe there is anything that could leach out into a viv and disturb the inhabitants from the Great Stuff product. Most keepers I know cover the GS with GE Silicone II Window and Door and put the substrate to that. I never did it to the GS Foam since I let it completely cure then sculpt in the cracks, shelves, planting locations and such since the GS expands, then silicone the whole thing and cover and press in the substrates.