What's up with my tapwater PH?

V1xIII

AC Members
Jul 11, 2008
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So here's the deal,

My tapwater PH when tested with an API high range liquid PH test is 7.4 dead on, which is the lowest the test goes, so for all I know it could be even lower out of the tap.

I've been fairly baffled as to why my tanks never, ever have a PH lower than 8.0, but since I recently noticed one of my tanks at around 8.3-8.4 I started becoming more concerned and wanted to figure out why.

I of course assumed it may be something in that tank that was causing the PH to rise, either plastic decoration or gravel. So I pulled a couple of the plants out, put them in a plastic bowl filled it with tapwater, and filled a plastic cup with the same water to use as a control sample.

After a couple days I tested the PH of the water in with the plants, not entirely to my surprise it's PH had risen to the lower 8's. I then tested the control water, and surprisingly it's PH was even higher than the plant water.

I then realized my test was stupid because regardless of the plastic plants being in the water, both the plant water and the control water were in plastic containers as well and ended up with higher PH. So for all I knew, all plastic made PH rise.

Once I realized my test was flawed, I put some tapwater in a GLASS and let it sit for 2 days. Remember, my tapwater has a PH of 7.4 or less out of the faucet...

So what was the PH of the tapwater that sat in a glass for 2 days untouched, and without any additives?..... 8.3

Does anyone know how that could possibly happen? And I guess more importantly what I can do about it in my tanks? According to crappy dip strips, my tapwater has very high GH and KH, so it doesn't change PH easily, except for apparently in the wrong direction for no reason....
 
Yes- it is likely disolved co2 in your tap water. When you let it sit the co2 outgasses and the water's pH rises to its true level. You cant test this faster by filling a glass with tap, drop in an airstone and let it bubble for 60 mins or so and test.

My water comes out at 6.3 but rises to 7.4 when the co2 outgasses.
 
Interesting, makes sense now. Never heard anything about tap water doing that before.

Thanks for the response.
 
yep, pretty typical.. tapwater right out of the tap is inconclusive for testing because of that.
 
It is always best to at least let your tap sample sit out overnight in a shallow dish, then test it. Not uncommon at all to see it rise.
 
At least I can stop worrying about the stuff in my tank for the most part. Thanks again.
 
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