I have a 450 african cichlid tank (it has a lot of plecos and synodontis to) and I am using gravel for a substrate. I want to get fine sand so my peacock cichlids can dig, but i don't know what kind to get or if i should get sand. I read sand can create sulfuric acid and that will lower the pH if it is sitting for to long without being stirred up. What kind of substrate should i use?