PH Meter : De-ionised v Distilled water

itiwhetu said:

Distilled water from a pharmacy, Chemist, drug store, what ever you call it over there

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Lynnzer said:

I got it sussed. I used distilled white vinegar 5% acid and a known ph of 2.4 to calibrate. In which case my water supply is at 7.00 ph. Only the GH messing things up at over 300gh

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1. How accurate is it really?
2. How easy is it to fool?

1. RO water in a glass: KH=0. pH reads 6.25. Seems a bit low but hey its uncalibrated. RO has been standing in a storage tank for 24 hours as I did my water changes yesterday. I would have expected the pH to have dropped from when it was produced, but not that much.
2. Community tank: KH=0. pH reads 5.25. Old established tank with wood, fish and plants. Results are consistent as I would expect it to be more acidic than pure RO.
3. Thai tank: KH=0. pH reads 5.8. As above and not really surprised. Remember I don't care about the number as its probably wrong, but higher or lower still makes sense.
4. Office tank. KH=0. pH reads 8. Tank is only a few months old, inert sand, plants and fish. The difference in this tank is I have a spraybar above the water line so there is a lot of surface disturbance (fairly low flow). Lots if tiny bubbles in the water. I am sure someone will suggest this drives out the CO2 but the bubbles and surface exchange are air, not oxygen. Even if the CO2 is reduced that is a 100 times reduction (at least) in hydrogen ion concentration. And pH does not go up in a biological system. Repeated several times with the same result.
5. Nano tank. dKH = 3, pH = 7.2. Roughly what I would expect. The KH is low but as I do a 75% water change every week that should be enough to keep it neutral.

seangee said:

So I got mine out after seeing this post and ran a few tests without calibration, after all without calibration it should still get higher and lower right. But this raised 2 questions.

1. How accurate is it really?
2. How easy is it to fool?

The good news is I got consistent results on multiple readings in the same tank, many of the reviews suggest very inconsistent results. But there is something odd.
Here are my results:

1. RO water in a glass: KH=0. pH reads 6.25. Seems a bit low but hey its uncalibrated. RO has been standing in a storage tank for 24 hours as I did my water changes yesterday. I would have expected the pH to have dropped from when it was produced, but not that much.
2. Community tank: KH=0. pH reads 5.25. Old established tank with wood, fish and plants. Results are consistent as I would expect it to be more acidic than pure RO.
3. Thai tank: KH=0. pH reads 5.8. As above and not really surprised. Remember I don't care about the number as its probably wrong, but higher or lower still makes sense.
4. Office tank. KH=0. pH reads 8. Tank is only a few months old, inert sand, plants and fish. The difference in this tank is I have a spraybar above the water line so there is a lot of surface disturbance (fairly low flow). Lots if tiny bubbles in the water. I am sure someone will suggest this drives out the CO2 but the bubbles and surface exchange are air, not oxygen. Even if the CO2 is reduced that is a 100 times reduction (at least) in hydrogen ion concentration. And pH does not go up in a biological system. Repeated several times with the same result.
5. Nano tank. dKH = 3, pH = 7.2. Roughly what I would expect. The KH is low but as I do a 75% water change every week that should be enough to keep it neutral.

So at least it produces consistent results (at least mine does). But here's the kicker. Next I waved API test strips at all 5 sources (also multiple times).
The nano tank showed a pH of 7 - as expected.
The other 4 sources all showed a pH of 6 which is as low as the API strips go. This includes the office tank (test 4).

So my only conclusion is that some factor in the office tank (bubbles???) is fooling the meter into a false reading.

I am not overly concerned and will continue not testing pH because I really don't care what the numbers are - but for those that do this may not be the best option.

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Guyb93 said:

Isn’t a KH of 0 bad ? Iv asked this before ,don’t you need some level of KH to stabilise the ph?

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