People obsess over ph too much. Are your fish and plants alive? If so ph is probably ok, it's mostly a yes or no question. Some areas have water or dirt with very low or very high and some species require very low or very high but you'll know if that's the case. For substrate in african cichlid tank shells are the best by far. If you're still worried about ph they are virtually pure calcium carbonate, crush a couple and that's as hard as it gets. Aside from that they leave lots of space for the inevitable fry to hide in and are easy to clean. Also lightweight and cheap (or free) to aquire.