0.5....thank you....that's what I needed to know..

It will take several days and a BUTTLOAD of ph down to beat it into submission but eventually your hydroton will bow to the correct ph. You're getting the idea of why I hate hydroton and my other reason for disliking it is that it seems to encourage fert buildup in my plants and cause problems later but I seem to be the only one that happens to for some reason. On it's plus side.....it's exremely lightweight which is nice and it repels algae very well.

As for your tap water it sounds ok......try one other thing for me if you would. Take your water and add some nutes to it....say enough to take the ppm to five hundred (you're tap water starts at 240, correct?) Then adjust ph to 5.6 and leave overnight....check again tomorrow. Hopefully the ph buffers in your nutes will keep things at the ph you set it to......that's the entire point of what we are trying to accomplish here.......a stable ph.....and we are testing to see if your tap water will hold one. My well water would creep up above 7.....sometimes to 8 no matter HOW much ph down I added. This is what we want to determine with yours.