The OP should keep in mind that not all tap water is created the same.
Keeping shrimp alive and keeping thriving shrimp, which they seem to want, are two different things. Hardness, dissolved solids, temperature, pH and oxygenation all play a role in shrimp health and it's important to remember that. A pH of 6.9 is not ideal. (Yes, I get that it works for you. But it's not ideal or recommended by most.)
I keep CRS with normal tap, use a PH buffering substrate like ADA aquasoil amazonia. My ph is 6.9 and my CRS/CBS are doing fine.