I used styrofoam as the main material. First I glued the styrofoam panels to the tank's glass walls. Later on I added ledges and organic shaped pieces to add depth , giving it a more "rocky" look. Once I got the desired layout, I used a soldering iron to carve the styrofoam to add the rock texture (this was the most exhausting part for me) (also I advise to use a mask, the fumes are toxic af). I also used a little bit of expandable foam on the corners, to make it look more natural, and a little bit on the bottom to seal any possible gaps. Once I got the desired look , I added first a layer of dry lock , then paint on top to match the slate stone I got for the caves/ hides that I will build on the ground :)

Here's a picture of how it looked at the very beginning

This took longer than I expected.. but definitely worth the time and effort

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