Silica sand is what you want. You need sand that is non-reactive to an acid environment. White play sand works well, but I wash it with acid before I use it in an acidic tank. It then takes several days to stabilize the pH to get it to settle down and maybe a week or more to get the nitrogen cycle going. I use snails and fish for that. If you already have a good acid tank going, a scoop of sand from that will kick start the process. You need something alive and food to keep the bacteria fed.
I use endler's guppies as they are tolerant to a wide range of pH. I pull them out before I put in small shrimp.
Breeding Crystal Red Shrimp
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