Tap water changes Ph

Stoner1993

Hello,

My tap used to have a pH around 7.5 but when I tested it today before a water change it is at 8.2. I have a 14gl tank which is currently at 7.2 due to th driftwood in it. What would be the best way to lower my tap pH so I don't have a big pH swing during a water change. Below are my full tank and tap parameters.

Tank:
Temp- 78
pH- 7.2
Ammonia- 0
Nitrite- 0
Nitrate- 20ppm
Kh- 3
Gh- 4

Tap:
pH- 8.2
Ammonia- 0
Nitrite- 0
Nitrate- 0ppm
Kh- 2
Gh- 3
 

MacZ

Before looking at how to change things, maybe first check how this can even happen. Going by your KH a pH of 8.2 is unlikely from a physical/chemical standpoint.

So first leave a glas of your tapwater stand overnight and test again in the morning.

Secondly the likelyhood your water provider adds something to raise pH as an anti-corrosion measure to keep maintenance on the public system down is high.

Thirdly to make sure this is not a testing error, how to you test and is the test you use still good? (Check the best before date.)

And finally, with the hardness being generally low I would not expect the difference to have an impact during waterchanges. Strong pH-swings during waterchanges are unlikely.
 
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Stoner1993

Thanks MacZ!

I thought a kh of 2 and pH of 8.2 was strange as well. I used API liquid tests kits and did both the low and high pH test three times, dates are still good.

Good idea on the off gasing. I currently have a bucket of tap water with an air stone in it. I will check it after a couple of hours.

Also need to do some digging into my local water supply.

Thanks again!
Ok so after only half an hour in bucket with an air stone the pH is down to 7.2, which is what is has been in the past. I checked the tap water and it is still reading 8.2. I am curious what is off gasing. I know CO2 can make water more acidic but I don't know of a gas that can make water more basic.
 
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MacZ

Good idea on the off gasing. I currently have a bucket of tap water with an air stone in it. I will check it after a couple of hours.
[...]
Ok so after only half an hour in bucket with an air stone the pH is down to 7.2, which is what is has been in the past. I checked the tap water and it is still reading 8.2. I am curious what is off gasing. I know CO2 can make water more acidic but I don't know of a gas that can make water more basic.

So it is as I thought.

Usually CO2 would gas off when the water is especially acidic. My thought was the opposite. With that KH the water should be picking up more CO2 from the air, bringing it to the actual pH. Because KH, CO2 and pH are in constant equilibrium. And this test has simply proven my theory.
 
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