water testing

[Fred T. Washington]

How long should I wait after a water change to do a water test?

[MatsP]

Depends... What are you testing for, and why do you think you need to wait at all? [Obviously, it will take a little while for the water to mix up properly, particularly in a big tank - it takes my 400 liter/100g tank about 5-10 minutes to have the same TDS all over the place when I pour in a bucket of re-mineralized water after topping up what I removed during a water - change].

But besides that, I don't see why you would have to wait, unless there is something specific that I don't see directly (I do know that some additives interferes with tests, e.g. some of the ammonia absorbing additives still show up the ammonia when you test for it - but waiting won't actually fix that particular issue unless the filter takes away the ammonia).

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Mats

[Bas Pels]

Apart from the mixing problems Matts referred to, the chemical reactions involved are either quite rapid, or very slow

If I were to pour a lot of acidic water (pH 3) into a ph 9 tank (without fishes, don't worry), I would see a rapid pH drop to, say, pH 7. Than it seams to stabilize

However, the next morning the pH will be back to close to 9 - due to slow reactions with the substrates

Still, were I to lower any pH, I would measure the fast pH drop - to acertain not too much acid is used (max drop 1 point) and the slow result, to acertain whether I had finally gotten a result (the disired pH lowering) or not

[Fred T. Washington]

I test for pH, ammonia and nitrate. Testing right away would be no big deal then? I was wanting to make sure the new water had "stabilized" and mixed in with the original water. Apparently that is not necessary? My tank is recovering from some out of whack parameters and I wanted to make sure I was getting accurate results on its progress.

[MatsP]

As Bas explained, there are two types of chemical reactions: Fast ones and slow ones. So, for things like nitrate and ammonia concentration after a water change, it should be fine to check immediately after the change - as it's just diluting it with water.

The slow reactions is such things as "calcerous rock dissolving in soft water" - and in that case, you do have to check the value after some time - 12-24 hours.

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Mats