It's not what is recomended to calibrate ,BUT if your meter can adjust and read the 800 PPm solution then it is telling you right. If your tap water is from a well that is not to bad. 200 is considered hard water. My little bro's well water is 160 and he runs it through a britta filter and gets it down to 90. It's working for him. I got a water distiller from sears for 100 bucks ,it's a pain to make water all the time but the water test about 8 to 10 PPM's and low PH. RO filters to hook up to your house water will do about the same, just replace filters 1 or 2 times a year. Look around there are good deals on them . The one I want is about 200 bucks but you can find them cheaper on ebay. If you buy water go distilled water , spring water is not regulated. Your almost there. The meter is good if it reads what the solution is. How's your PH ? My bro had just started and his PH was 7.6, I brought it down to 5.8 and his plants took off.