40 breeder with your water you could do blue acaras, small gymnos, Krobia sp, burjuquina sp, might be tight for geoohagus steindachneri complex but probably doable, cichlasoma dimerus and other sp, australheros sp.
Could look into Central American species as well most of the cribroheros would work, as would cryptoheros / amatiania, or thoricthys.
I keep or have kept almost everything I’ve listed in a tank that size with water like yours. There’s way too much stuff to keep well, healthy and breeding in that water to even bother considering RODI
for your plants. You need to get ahold of oyster shells, drill 1/4, or 3/8“ holes in them and stick your plants stems/ root ball down through the holes you’ve drilled. You now have a shield around the plant that they can’t dig up. That’s how I plant my cichlids tanks. Some
Cichlids will still break all the stems off some won’t