Where can I get aquatic moss? I've never heard of that before. As for the substrate, I think it will be pretty moist. I wanted to ask you, I couldn't find any epoxy in any of the hardware stores, but i was looking at this Minwax polyurethane sealer and this guy came up to me and said the 'spar urethane' was what people use on their boats. He asked me what I needed it for- he didn't work there so I thought it was strange- so I told him I was using it to seal a waterfall in a viv I was making. I could barely get a word in edgewise so I was wondering if you knew if it was safe to use (on the waterfall) with the frogs.