Hi Mark, think you've inspired me here... I'm currently in the process of a lengthy renovation but once done and back onto tanks, I'm going to grab a few handfuls of that moss I mentioned& give it a try submerged, gut instinct is telling me that it will work as its from a very wet area in Loughrigg in Cumbria. Your Iwagumi idea sounds fab mate, go for it. It'll make an awesome journal as well. Cant wait to get my hands wet again!