Looking good - I use pool filter sand with an Eheim canister and no problems. The issue is to make sure you don’t accidentally get any of that sand between the acrylic and whatever you are cleaning the algae off with. I have a few unsightly scratches because of that. Nice looking tank - who did you get to make it, and is that 1/2” acrylic? If so, do you se any bi int at all? I regret getting my 300 tall - wish I had done a 240 or 300 wide. It is a pain to clean and weighs a ton as had to be 3/4” due to the height. The benefits would be the allowance for greater water change percent and volume - but that’s about it.