The other option im testing out on one of my smaller tanks at the moment is to fill the bio media tray of my canister filter with coral rock rubble, my LFS sells broken up dry coral rock, i bought some, smashed it up more with a hammer, rinsed it with tank water at water change time and filled one of my media trays with it.
I only installed it last night so ill be testing the tanks PH over the next month to watch how it goes with this setup, the coral rock should act as bio media filtration as well as being naturally high in PH