pH test discrepancy

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tetra_girl

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Dec 21, 2002
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Has anyone ever gotten two different pH reading from two different test kits?

I have always used Jungle 'Quick Dip' pH strips, but I just recently got a new Hagen Mini Master Kit.

My main tank had tested with the strips at 6.8 yesterday and I decided to check my quarantine tank today with the new Hagen pH test. It came out to 7.0. So I was curious and decided to check it also with the strips and the strips read only 6.2!

I then tested the main tank again with the strips (still 6.8), but the Hagen test came out 7.6!

That's 0.8 difference on both accounts. Why is there such a large discrepancy between the two tests?

Anyone ever experience different test kits giving such different results? :confused:
 
Yes indeedie, me too. It's a bummer, you don't really know what you've got. I use Aquarium Pharmaceutical's liquid pH test kit, and its results are consistent. But when I had my water tested at two different lfs, they got two different results, and one of them was using the same test kit I was!! The other one said liquid test kits are never accurate, and he uses only the ground-up-tablet kind, which yielded a different result, of course.

Very confusing.

I don't really trust the test strips, because the range of readings on them is so wide. I like to narrow it down a bit more than that. I'd be very grateful to anyone who could say with certainty what kit gives accurate results.

-- Pat
 
I'll tell ya! In my High School Lab, we have pH probes. Plug on of these into your TI-83, and plug this into your computer. I'm not sure if you can eliminate any of the equipment, but I know that setup works. Expensive, but accurate to the hundreth. Also resuable, so if u already have a computer and graphing calculator, it wouldnt be a bad idea.
 
Hmmm....that is a bummer.

I myself am kind of biased towards the strips because I know it's litmus paper- which is what I used in the lab for biology and ecology (many moons ago when I was in school ;) ).

Litmus paper was the standard for pH testing that we used (and yes the paper is suppose to cover anywhere from partial range to the full pH range, from 0-14 actually), but all the other tests for hardness of water, and various elements ie ammonia were liquid reagent tests just like the aquarium kits.

I do suppose though that there are different grades/qualities of litmus paper too, top notch lab quality and not. The strips are obviously not the same as what we had in the lab as the range they cover is not very wide and it's glued to a plastic strip (our lab stuff came either in plastic tape dispenser like rolls or just cut paper strips and was full range).

Oh well, glad to know it's not just me but not happy that it's not just a bum kit. :(

Anyone know how these different kits stack up against each other/which is more accurate?

Or anyone ever take some litmus paper from the lab/buy some from a scientific equipment supplier and compare results???
 
I have some sticks that test the Ph, hardness, and buffing of water. I use them occasionly, but I use Aquarium Pharmaceutical's liquid test kits regularly. When I compared the two results they were similiar, but the water here has a high Ph and is very hard. I'm at work and can't remember the name of the sticks. I'll edit them on the this thread later.
 
Opps, there I go again posting sooo slow. :p

Ya, I remember probes for various things and they were hooked up to a little meter device in a suitcase (for work out in the field). I think ours were mainly for salinity though....don't quite remember.

But if someone that has access to this kind of equipment and also has some of the commercial aquarium test kits....

Someone could bring in some water and do a comparative test across the board using the different tests and see which if any came out the same as the lab equipment readings? Or just swipe some litmus paper as I mentioned earlier. ;)
 
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