Matching pH during water changes - best method is (not) a chemical? - GTA Aquaria Forum - Aquarium Fish & Plants serving the Greater Toronto Area.
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General Freshwater Discussion For all topics relating to freshwater fish to the in's and out's of maintaining a freshwater tank.

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Old 08-30-2019, 02:24 PM   #1
TMonahan
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Question Matching pH during water changes - best method is (not) a chemical?

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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Old 08-30-2019, 02:43 PM   #2
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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…. 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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Old 09-06-2019, 04:41 PM   #3
Karin
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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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Old 09-12-2019, 03:23 AM   #4
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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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Old 09-18-2019, 09:27 AM   #5
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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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