Yes, you're right it's a bit of a problem, but is this the same water you have been using all along? Perhaps sittiing out lowers your ph (although it really shouldn't have too much effect on ph itself) or the soil you've been using has good ph buffers in it. Or....or ...or.....

You really need Stinky here.......you're getting out of my knowledge range in soil in a hurry. I would go ahead and check runoff ph......see if your soil is buffering things at all or not.....and Stinky should be back in the morning to help you. I'd hate to give advice I'm not sure of because I think you recently DID transplant to fresh soil didn't you? i really don't want to make things worse here.