I noticed that they are growing already! I'm going to get some pool filter sand for their tank, I still have some black diamond blasting sand, but I think the lighter pool filter sand will look better in their tank.
I'm going to add some terra cotta pots for them to hide in after I add the sand. I was having a hard time finding pool filter sand because I wanted to get is locally since shipping is expensive, but thankfully I found it on Ace Hardware's website, with free store pickup, so I ordered one 50 pound bag. I think that will be enough for the tank, I used slightly less than a full bag of the Black Diamond sand in my other 40 gallon tank, the one with my Flowerhorn.