Do you have a way to check EC? I do on my meter but I never really use it...always go with the ppms....I have actually had 2 of my 8 today come up with a lower ph but Im wondering if perhaps I used too much ph down yesterday.....obviously that wouldn't be your problem...just babbling....if I see it again I will check EC on my plants. I'm not sure that there ARE buffers in tap water.....just shades of either acid or alkaline with no stabilizers. Or perhaps more than shades......