Discrepencies In Water Testing

[daveyravey]

Hi folks,

Does anyone else get different readings from different test kits ?

I have been using a Nutrafin test kit since i started this tank up & the readings seemed to be ok, keeping nice & steady.

Last week, i got the problem with that red rock ornament sending the PH low, so i got that all sorted, then on Saturday afternoon the PH dropped again to 5 & stayed there for 3 hrs.
I went out & tried to buy some crushed coral (as advised) to add to the filter, but alas, my LFS didn't stock it ! I asked them if they stocked something to lift the water's PH value & they advised me to get some API PH Up to fix my problem, along with a 50% water change. ( i thought this was a bit strange).

I duely bought the treatment, went home, tested at 6, added 1ml to the tank, left it 1hr & retested......6 !

Reread the instructions, added another 1ml, left an hour & retested....... 6 !

At this time i hadn't changed any water, so i drained 10lt & replaced with dechlorinated tapwater...waited an hour ...again, retested....6

By this time, it's gone 9pm & i've given up, as everything else tested fine & the fish look happy enough, which is a good sign in my book.

It was the same on Sunday, but i added another 1 ml twice through the day, but the PH never came above 6 along with 5ml of Ammolock as the Am was reading 2.4....tested an hour later & the Am had dropped to 1.3, but the PH was still 6.

Today, i had an idea..... buy another test kit to see if there was any difference, plus the origional kit is getting a wee bit low on fluids.
Couldn't get another Nutrafin, so bought API master.

Test 1 - Nut - 6.....API 7

Test 2 - Nut - 5..... API 7

That shows a big difference in PH values & i don't really know what to make of it to be honest.

Anyone else had this problem ?

 

[coldcazzie]

I have had that problem too.

I have a nutrafin wide range pH test kit which shows my tap water at 6.5, but the API pH test kit shows it at 7.4. I happen to prefer the API ones so have always used that one...

I was quite surprised - a difference of nearly 1 on the pH scale is quite a bit when you're talking about actual acidity/alkalinity of the water. I didn't think the test kits could get away with being that different so I discounted the nutrafin one because I don't like it lol! (kinda like sticking my head in the sand I know!) I'd expect small differences, but not that much.

What would really interest me would be a lab test to show what my tap water pH actually is and comparing it with both the test kits, and some other regularly used ones like tetra/saliferts.

 

[drobbyb]

Was the nutrifin test out of date possibly? I would expect a small difference, but 1 point is a whole lot different when it comes to pH, like Caz said. I've always used the API tests, so I have learned to trust them.

I suppose if you want accuracy, a digital pH meter would come in real handy, but they cost alot.

Did a little research, and some of them are affordable. Might be worth looking into.

 

[Truck]

even digital ph meters can be un accurate, unless you have lab grade

 

[nickelplates]

All aquarium test kits are a pretty blunt instrument they give a very rough guide although pH kits are generally more accurate than the Ammonia/Nitrite/Nitrate ones. Best to pick a kit you like and always buy that one as that will give you a good idea of changes in your water which is usually more important than absolute values anyway.

Also bear in mind that the pH scale is logarithmic so anything between 6.5 and 7.5 is vey close to neutral but going out to 5 or 9 say is a big change. If you really want to know try http/en.wikipedia.org/wiki/PH but it is a touch mathematical.

 

[daveyravey]

Did another cross ref check this morning

Nut - 6.5

API - 7 lower & 7.4 upper.

The Nutrafin kit isn't out of date, it's good til april 2010

 

[coldcazzie]

To be fair - both my kits were brand new - the API one was about 2 weeks old at that point and it was the first ever test out of the nutrafin one!

As has been said - I think the overall trend of the tank water is more important than the actual readings, unless you're talking about extremes.

I use the API one because I happen to like it, and that's the one I was using before, I was just curious to see whether the wide range one would show it being slightly different because my tap pH is at the higher end of the API kit scale. I wasn't expecting the result I got, and I haven't used the nutrafin one since! I'd chuck it except I can't bring myself to throw something brand new away simply because I don't like it! lol

Anyone want a nutrafin wide range pH kit?! I'll do you a good deal lol