I have a 20 long and a 20 tall that i want to change to tile. How hard is it? What do you use to hold it down? I do have fish in both tanks right now. I have an extra 10 gallon i can put the fish in for no more then two days if i have to. The 20 long is my 4 and 7 year old girls tank. It is a tetra tank overstocked, have now banned there mother from buying more fish. Anyway the other has one pair of cons in it. After i tile the tanks if i do the tetras are going in the tall and cons are going in the breeder tank. Any help would be greatly appreciated.