Hi, Being a former fish keeper I am conversant with TDS and RO water and also ph issues and resolution in water. I am not sure if I were to use tap water how you would work out the tds for hydro because the base numbers for tap water (unknown to me in this area at this time) is number X so how do you work out how much nutes to use to make it usable. The nutes will say XXXppm but thw water will be XXXppm with no nutes. I am confused !! Is it just add nutes till you get the correct TDS? I mean does the waters natural TDS play a part in the final ppm ? PLEASE help cos I wanna do a dwc of flood and ebb after the heat calms down some.