Is that your tap water you're saying is 40 ppm and 7.5ph? If it is, I'd say just use that. 40ppm is nothing. Back in the day I was using tap water that was 300-400 ppm at times. Not ideal, but I was getting 2.25- 2.75lbs per 1000 watts. I'd always draw it into a 55 gallon drum and run a bubble...