API test kit liquid vs strips vs Co-op strips?

[NetBelleAnie]

So I set up my 55g, it's doing pretty good at the moment, but I keep having issues when testing my water.  When I use either the Aquarium Co-op or API test strips, my PH reads around 6.8 - 7, but when I use the API liquid test (high range) it says it's about an 8.  My KH is 4 and GH is 6.  Any idea what is happening?  All the tests are fresh, but I can't figure out why the PH reading is so different between them.

[tonyjuliano]

Ah... the API liquid pH test conundrum!

problem is that the high and low range tests are pretty much split at neutral, so if your pH is at the “high” side of the low test, or on the “low” side of the high range test, you have to run both tests (and even then it’s difficult to tell).

I settled on electronic pH testing as soon as they became economically feasible.  As long as these units are calibrated properly (which is easy to do), they will yield more accurate results.

you can get a decent one (with automatic temperature compensation) for around 20 bucks.

Don’t forget...  pH increases (and decreases) with temperature! So using the liquid kit can yield inaccurate results if the sample doesn’t remain the same temp as the source.

Edited May 12, 2021 by tonyjuliano

[Isaac M]

Hi @NetBelleAnie, good to hear the aquarium is doing well! As far as the testing, have you tried testing your pH with the normal pH API liquid test? The high range test I believe only detects pH above 7.4 but it will read as 7.4 if it is below. Given that both the test strips read the same, I would go with that but the liquid kit should be within reasonable range. I would try testing with the normal pH liquid test and see what reading that gives you. 

[NetBelleAnie]

4 minutes ago, tonyjuliano said:

Ah... the API liquid pH test conundrum!

problem is that the high and low range tests are pretty much split at neutral, so if your pH is at the “high” side of the low test, or on the “low” side of the high range test, you have to run both tests (and even then it’s difficult to tell).

I settled on electronic pH testing as soon as they became economically feasible.  As long as these units are calibrated properly (which is easy to do), they will yield more accurate results.

you can get a decent one (with automatic temperature compensation) for around 20 bucks.

Don’t forget...  pH increases (and decreases) with temperature! So using the liquid kit can yield inaccurate results if the sample doesn’t remain the same temp as the source.

Didn't realize the PH changes with temperature,  I keep the tank at 75 but room is usually around 69-71 where I test.  I'll look into a digital one, it's hunting that's the hard part.

4 minutes ago, Isaac M said:

Hi @NetBelleAnie, good to hear the aquarium is doing well! As far as the testing, have you tried testing your pH with the normal pH API liquid test? The high range test I believe only detects pH above 7.4 but it will read as 7.4 if it is below. Given that both the test strips read the same, I would go with that but the liquid kit should be within reasonable range. I would try testing with the normal pH liquid test and see what reading that gives you. 

I used both the tests, and after repeatedly finding the regular one having the hightest reading possible while the high range before would be at the absolute lowest, I started testing only the high-range as the tests started leaning more alkaline.  I'm pretty sure the mixture of Onyx-sand and Eco-complete and my 7.4 tapwater are combining, but I would assume that the 3 little pieces of malasian driftwood's tannins would start counteracting that.

[tonyjuliano]

17 minutes ago, BIG GREEN said:

one time my 100 gallon KH reading was a 0 and the ph dip down to 6, I never figured out why that happen.

Low carbonate hardness (KH) will make your pH swing like crazy.  Carbonate hardness acts as a buffer.

[Turtle]

Stay with the low kit for now. Plan out your tank so you know what you want to do. Looking forward read about the fish you want to keep. You will find balance in time.  PH of your water source  is important so you have a baseline. Test kits are basic guidelines for display tanks. The deeper you go into fish type the more it will become important. Turtle 🐢

[LaurieinIA]

I’m having similar trouble with test results. 

Not long ago, I needed to replace testing supplies and I changed from the Fluval test kit to API one. I did this because I could never confidently read the Fluval results - especially nitrates.  I wasn’t too concerned about not 100% accurately reading the pH as my only tank at the time was African cichlids... as long as it got past greenish yellow and seemed consistent - I’d take photos to compare - I accepted it as high enough.

Moving forward to today... I still have the Fluval pH test (the others have run out) with a result of 7.0, maybe 7.5, and my API test shows a solid 8.0.  This is in a community of tetras, so the difference could/should be a problem.  They seem fine overall, but I have lost a few within a couple days of adding them, so I’m wondering more if my pH is really 8.0.

I don’t know which test to trust and if the readings are that different on pH, can I trust the other test readings?

I’ve talked to my LFS and they don’t have a great opinion of the API tests.  They don’t even sell them.  Of course, they are willing to test my water (which I will have them do today), but it still doesn’t give me the answers I need at home.  I’ve tried tetra test strips in the past and have the new COOP ones as well... I can’t confidently read pH on those either.

[Patrick_G]

Would it be possible to “ calibrate” your liquid test based on a solution with a known PH? 
A one molar solution of baking soda at 77 degrees should be PH 8.3 

 

 

[CT_]

I have the exact same problem with my co-op test strips.  co-op strips read about 1ph lower than my API kit, my cheap but calibrated electronic probe, and the 1000$ calibrated probe at the university.  most recently its been reading <7 and my other methods read ~8.

 

In the live stream a day or two ago cory implied errors are user error.  I've done a lot of fiddling trying to get the test strips to match analytical standards that I have and I can now get them pretty accurate on everything but pH.  The tricks I've found is that you actually have to wait the full 1 min, but not too long after that 1 min or the color keeps changing, nitrate especially for me.  I've also found that the pads interfere with each others readings if a drop of water bridges them after you take them out of your tank.

[tonyjuliano]

6 hours ago, LaurieinIA said:

 

I don’t know which test to trust and if the readings are that different on pH, can I trust the other test readings?

This has always been a problem for me with any of the liquid test kits.  They have always been fine for testing ammonia, nitrite, nitrate, KH, GH, etc., but pH - especially in the range of 7.0 to 8.0 - has been problematic for me.

Having pH tested at the fish store isn’t practical (pH changes with temperature, and by the time you get your sample there, it will most likely have changed).

Best solution I have found - and its a very good one - is a handheld digital tester.

Keep it calibrated (which is easy to do) and you have accurate results at your fingertips.  A real number, no interpretation of color scales.

Just make sure you get a calibrate-able model, with automatic temperature compensation.  About 20 bucks on Amazon. 
 

As a side note, it’s more important to have a stable pH level than an “optimal” one for a certain species.  Most freshwater fish (there are a few exceptions) will do just fine with a pH level somewhere between 7 and 8, as long as they are acclimated over time.

 

[tonyjuliano]

2 minutes ago, CT_ said:

co-op strips read about 1ph lower than my API kit, my cheap but calibrated electronic probe, and the 1000$ calibrated probe at the university.  most recently its been reading <7 and my other methods read ~8.

Obviously, if your digital tester and the lab model agree, then the strip is the “outlier”.

[CT_]

1 minute ago, tonyjuliano said:

(pH changes with temperature, and by the time you get your sample there, it will most likely have changed).

pH does not change with temperature that much.  depending on the solution, it might change 0.01 to 0.5 over a 25C change, most fish stores don't keep their thermostat at 125F.

[LaurieinIA]

@tonyjuliano I agree that having my water tested at the store is not a 100% accurate representation of what it is at home. My plan is to run my tests along side theirs so I can see the differences. We will be testing the same exact water.  Once I know where I’m at, I feel I can watch the trends accordingly. 

Edited May 12, 2021 by LaurieinIA

[CT_]

1 minute ago, tonyjuliano said:

Obviously, if your digital tester and the lab model agree, then the strip is the “outlier”.

indeed.  but I'd really like to know why the strip disagrees.  Maybe there's something relatively rare in my water that directly interferes with the indicator dye.  I'd love to figure out what it is.

[tonyjuliano]

2 minutes ago, CT_ said:

H does not change with temperature that much

No.. the difference is not significant, but it’s just another variable to skew results.

And the “change” differs depending on whether your solution is more acid or more basic (more basic = more change).