I did a search but didn't find much in the way of current threads on this topic. I'm in the process of a DIY inground build and I'm getting quite a bit of differing info regarding the base. I've been told only vermiculite works, or only concrete on the flat and slopes and vermiculite on the sides of the hopper, or only use perlite and cement, or sand and cement or just sand. I'm trying to sort it all out. From what I can tell vermiculite is kind to the liner but not the wallet, sand and cement is easier on the wallet but like sandpaper on the liner, concrete is not that cheap and will not be fun to land on, perlite being a volcanic glass isn't the best choice for the liner but is cheaper than vermiculite, and sand is easier on the wallet and the liner but is likely to dent. My soil is all nice clean sand and there are no groundwater issues to contend with. If I just go with a sand bottom, I'll save a bunch of money but I will definitely need to plan on some work when the liner gets replaced. But many builders have cautioned me against going this route. I'm getting a 27 mil liner so I don't see how this will differ from every inground pool built 10 to 15 years ago.
I don't want to cut corners for the sake of a few bucks but with the materials running around $1,100 for the vermiculite and cement I don't want to spend all of the money and time if I'm not going to see much benefit. I can buy the perlite and cement for around $750, and I can use material I have on site for a sand bottom.