The larger tank has dorest pea gravel (which is rounded small smooth pebbles). When I was setting the tank up asked if ok and some said should be on the larger cories. I have had no problems and had them since ohhhh october timeish now? I do inspect barbels etc daily to check no problems and they have been perfect. I will say though having seen the others react with sand, certainly would do this the second time round When it comes to the pygmy cories it is essential to have the sand. The breeding tank I hope to have going soon has coloured gravel and completely unsuitable, will be doing bare bottom or sand LOL Thanks for the compliment Im not the best with plants!