Don't use cat litter. Keep it simple...dirt and gravel.Please do not use kitty litter! It is for cats, not aquariums. It quickly turns to mud and reacts with the soil to generate aluminum toxicity. It also forms a dense, thick, gooey mass. I don't think mineralizing will help. One hobbyist (maico996) has already described a disaster using a kitty litter soil mix. He had to tear the tank down and start over.