# Matching pH during water changes - best method is (not) a chemical?



## TMonahan (Aug 29, 2019)

If the tank your running is at a higher pH than your local water supply (ie. tap water)... what is the best way to replace the water during a WC so that the pH remains stable? For my example, lets say the tank is 7.6, and the local water supply is 6.6 pH.

If I'm running a tank that has crushed coral or limestone inside it, my understanding is that over many weeks these substances slowly leech into the water creating a natural stable pH. The water being replaced after a WC/vacuuming doesn't have the luxury of being slowly tweaked by coral or dissolved anything... so I'm supposed to use a pH riser chemicle like pH Up to try and match it before dumping it in the tank?

Lets say this *is* the preferred method of matching pH... doesn't the pH boosted replacement water crash after a bit of time or is that not a worry?
pH booster (like API pH up) or baking soda... either way - how does that water now react with the water that was left in the tank which was naturally raised via coral/limestone?

When talking regular WC, I'm thinking 15% - 25% weekly. Water is also treated with conditioner like Prime.


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## tom g (Jul 8, 2009)

*ph*

my recc is to stop chasing the numbers take a step back go back to basics 
stop adding things to tank to correct this and that . 
jmho&#8230;. adding additives to tanks is band aids most can be controlled thru water changes ...sometimes adding stuff just makes a bigger mess and u cant correct the issue created .


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## Karin (May 21, 2019)

Ph is measured on a logarithmic scale, so a normal water change shouldn't really affect it that much.
Have you actually measured it before and after changing the water?

It's been a long time since I've done the actual math, but if i remember correctly, if you replace 1/2 of the water with ph that is 1 point lower, it shouldn't go down more than 1/4....


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## Kajendra (Dec 12, 2010)

I don't know how to solve the issue on hand, but if you want the math...

If you change 50% of the water with a ph of 6.6 water and 7.6 (tank water)
Your new ph will be 6.86

If you do a 25% water change with a ph of 6.6 water and 7.6 (tank water)
Your new ph will be 7.09

10% Water change would result in a ph of 7.32

What should also be considered is how long the crushed coral takes affect on the ph.

A helpful link that might shine light on your later questions might be here, but it is a bit wordy...
https://users.cs.duke.edu/~narten/faq/chemistry.html
The link also explains why it's suggested to avoid additives when possible

Good luck!


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## BillD (Jun 5, 2006)

If the water is the same TDS, which is likely from the same source, the pH doesn't matter. High tech co2 injected planted tanks have a pH swing daily.


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