Ah ok, I wasn't sure which you ended up using. I think thinner stuff might compress a bit more for you if you think there is still a bit of a gap.

gonna leave it a day or so with water in it to see how it goes. I think if i used the high density pink or blue foam from home depot, it would not have compressed. this stuff is nice and soft

Mine kept on compressing for about a week until it stopped. Then I bought self sticking rubber base (base board) and put it around bottom of tank to trim it out and cover the styrofoam. The rubber base is waterproof and flexible so it is perfect for that application. It is 1.00 a ft and comes in different colors. all depends on your taste...

Ooops, just saw your pic. You bought something different than I thought.

http://i79.photobucket.com/albums/j1...pshvfmfm7g.jpg

http://i79.photobucket.com/albums/j1...pszaduphyv.jpg

http://i79.photobucket.com/albums/j1...psdsv81thc.jpg

i will definitely look into that, as the styrofoam dosent look too bad but would still like to cover it up

I also bought black corrugated plastic and put it on top of styrofoam so that my tank bottom was black to match sand color, that way if the sand moved and exposed the foam, you could not see the color of the styrofoam. Again all depends on what you are doing...

Thats correct. I remember reading a tank builders thread on it, that suggested using only the white for the reasons mentioned here. That being said, I once used pink and it seemed fine but mostly the white and use some type of black edging material.