Tap water question

I was wondering what all of your tap water reads as far as pH os concerned. As you may (or may not) know, I made a bunch of aragocrete dry rock. My pH test kit reads from 7.4 to 8.8. Initially I was using RO water, which reads 7.4 going in and 8.8 coming out after 24 hours. I decided that it may be wasteful to use so much RO every day (would be about 45 gallons I estimate) so I went with tap tonight. I realized that my tap water is reading 8.8 before it even hits the rock, so basically my tap water is 8.8+ I wasn't necessarily expecting the tap water to be identical to the RO water, but I was shocked to see such a high ph and that water. Any idea of this is going to effect my end goal of leaching all the "bad stuff" out of the rock? I was sort of banking on being able to do a water test every night once the water has been in with the rocks for 24 hours in order to get some sort of visual as to when the pH finally starts dropping enough.

 

I did consider the phosphate issues but then I got to wondering what exactly is in cement anyway? I imagine I have a whole lot to leach out before I need to worry about it absorbing anything? I could be completely wrong. I was planning on using RO water for the last couple of weeks of the process when the leaching is much less rapid, compared to what it looks to be now. I am not sure my thinking is correct on that though. Thoughts?

 

Well that is what I don't know. Both read high, but all things considered, the PH kit I have access to doesn't really tell me a whole lot. I basically have a range of about 1.5 to toy with. For all I know, the ph of the rock water is actually 10, maybe more. I will say that it does irritate the skin, where just tap water doesn't. I guess a question to ask is what pH should I expect from my water if going in it was 7.0? I will say that visually there is definitely crap coming out of the rock be it sitting in circulating RO water or circulating tap. The self proclaimed chem guy at RC (Randy) said I could just add some vinegar to the water mix to help drop the pH, but he has yet to respond whether I should actually consider doing that or not.

 

Supposedly it will give a ph of around 13-14 depending on how much leaches out, so tap would work about as well as RO, at least for the removing of the high pH. Guess I just need to decide whether I want to go RO or not with in regards to phosphates.

 

So I thought I would update here. Apparently adding vinegar to the water to get ph between 6-7 is the way to go. Once the PH rises way back up it is time to do the water change.