pond shield

Hello All, I have no idea what I am doing.... No, I kid, but this is the first time I've built a tank this big. This build is a mixture of DIY and trying out new products/technologies. I've built the tank (8' x 4' x 3') out of 2x4s and 3/4 plywood. But I wanted a massive sump and external...

I'm planing on doing some DIY cave decor for my fishtanks but I'm really unsure what material to use. I've been looking at polystyrene, fiberglass or potters clay. I like the potters clay idea but I really don't want to have it fired I was wondering if I could let it dry for a couple of weeks...