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i might use it for a custom dock however my turtle is hungry all the time and i do not wish to take the risk

I wouldn't suggest it, only because they could very easily bite it and eat it. Now, if you could encase it in something, like glue rocks to it or something, that might work. I don't know if styrofoam leaches chemicals though.

It's not good to have him eat it because it isn't digestible and can cause impaction. Also, it's probably toxic.
Corkbark is a good option for docks. So it PVC with a tile on it.

PVC is your best friend here. There are plenty of fittings available for making a cool basking platform.

If you want to make a floating dock (probably not, but it was the first thing I thought of when I read "styrofoam"), you can just glue together a rectangular PVC shape and it'll float. Just drill out holes in a different part of the structure that's separate from the closed of sections. Slide metal rods through with suction cups at either end like the store bought docks have. Now you can customize the shape and it will definitely hold up better.

I made a PVC dock that hangs from the side of my tank. I'm going to build one that actually sits in the tank for my new 75 gallon.

Good luck!

Edit: made this:

wow!! Those are great! I'll have to remember this for when Mikey gets his big tank.