You may want to try some DW.
And yes, if you are trying to get the numbers of them up, fish are not good to mix. If you get too many RCS add fish and it should work out great. If you don't care about raising the numbers, the adults can live well together with smaller fish, like a Chili Rasbora. Even my other nano fish will snack on tiny ones, like Celestial Pearl Danios for instance. Beautiful fish though, and if you have a breeding tank and a show tank that is great.
The question relating to pH is also that they do get used to higher pH water for most types of fish. And locally bred and raised fish would be a solution.