I have a 55 gallon refugium. I use to have sand in it but realized that there was not enough in there to do good and it was trapping a lot of gunk. So I removed it and now just have rock and macro in there. It’s a lot easier to clean when it needs it. I just use my shop vac (for tank use only) to suck all the gunk out. I love having a refugium for my tank. It helps to grow pods and allows me to house fish and inverts in there if needed for a short period of time. I have my 2 brittle stars in there now. I’m waiting to redo my sand bed and rock work before I add them to the display. It easier to remove them and find them while in the refugium.