you don't need one because you're KH/GH are fine, along with the rest of your water params, no need to spend the money if the water is coming out like that. But if you're KH/GH were both, for instance, over 8 or 10+(Hard Water) or something, you'd probably want to get it to soften the water and bring the TDS down. You already have soft water in the range that the shrimp likewhy does everyone say ro system is the best and a must!!!!
why would i not need one ?