7 is ok for soil... 6.5 to 6.8 is better imo....you need to ph your water to know how to keep the soil at a particular ph, tho. If the water you use is 7 or higher, yes, you want to use a ph down to get the water in range to slightly lower the soil ph. Use baby steps tho....if you start tryin to get the ph correct in one step you may start it swingin back and forth and that's not good either!