H&M com100 ec meter, @ the 500 scale, that's calibrated with the 342 ppm and 1000 ppm H&M standards. Winter Tap water comes in at 172 ppm's, Just checked it. And it comes in about 100 ppm higher in the summer months due to the increase of chlorine use. I'm in Michigan, So we are drawing off the great Lakes for water. With a tap PH of 6.8 - 7.0 pretty much all year. But I do use a mix of tap water and --- I have a new 90+ condensing furnace that outputs lots of water @ about 3.5-4.0 PH winter and summer with Heat or AC usage. That water get pumped into 50 gal, food grade drums. And yes I use that low ph water for Ph down. And tap water for PH up. Hope that makes sense to you? I figure why waste it, Just going down the drain! It's just Condensation. I'v been doing this for several years now, It may sound complicated but its real easy. However remember each of my reservoirs is 15 gal's of actual water + Lots of Air! with Fine bubbles that's for 2 large or 3 med sized plants. With that much water and air my PH swings are very low. When I first started to grow I tried the 5 gal DWC bucket, I was chasing my tail with problems. So I went RDWC it was 100% better but grew tired of chasing Leaks, Root plugging my lines Cleaning all the buckets and lines and whatnot. So I went with single big Reservoirs Lots of Air, And my problems were gone. With the Quality of the water I have, My next move will be Coco drain to waste. Simpler to move the plants around, work on them, trim leaves-up and whatnot. And the MegaCrop is working great for those that use DTW Coco. Cheers and tight Buds and lots of air!!!!!!!
old large boating cooler that had a broken lid. Made a new lid out Plywood with short sides to lock it in place, With holes cut in for the baskets, 15 gal's of actual water. Even has a drain plug to connect a hose to for draining. 
Next move for me Coco drip to waste. Cheers and Tight Buds!!
