Conflicting dKH tests
 

Newbie here! I have a 75 gal display tank with dry rock, a 33 gallon trigger sump with .25lb Chaeto in the refuge section. Simplicity skimmer running during current cycle. The tank is nearing the end of it's first cycle with nitrite level at 0.1. I have been using Red Sea and Salifert test kits. parameters are as follows:

dKH=9-10 Red Sea test kit
Mg=1400 Red Sea test kit
Ca=425 Red Sea test kit

After running the Red Sea dKH test a few times, I wanted to try an easier testing method so I bought a Hanna Checker. Ran the test twice and got dKH readings of 6.7 and 6.8. Any thoughts on why the big difference in readings and what to do about it?:headwalls:

Watch a youtube video on how to do each test. I was doing red sea tests in a way that wasn't entirely accurate.

Also, with the Hannah Checker did you hold the button for the second vial to give it the three minute countdown?

What salt mix are you using?

Are you sure you are using/reading the syringe properly?.. you go by the plunger (bottom of the cylinder) and not the fluid level when reading it..
So the plunger may be at 1.0mL but the fluid only a .8mL.. you have 1mL of liquid and not .8mL

But yes.. try the videos to ensure you are doing it right and also post the salt mix you are using... They all state their "as freshly mixed" values so you should be able to compare to that too..

Don't consider .1 a big diff with regard to the Hanna readings. I've often seen a .1 or even .2 difference when doing tests back to back. Many reasons this could occur, all have to do with testing errors. Slight volume diff in the plunger and/or water volume, or dirty testing vial.

As for the 3 min count down, never heard of this nor is it depicted in the Hanna instructions nor videos.

I believe OP is talking about the difference between the Hannah reading of 6.7/6.8 and the Red Sea reading of 9-10.

Since this tank is new, and there shouldn't be much alk demand, and freshly mixed saltwater should be closer to the 9-10 dKH range, I would suspect testing error with the Hannah Checker. I haven't used Hannah checkers, so I can't help further than that.

With that regard I agree. I've seen big differences between the Red Sea and Hanna results. I never paid it much attention because both readings were within recommended parameters.

I only use the Red Sea for magnesium now since the Hanna are much simpler and faster.

Maybe there is an explanation out there for why they vary so much.

There is a 3 minute waiting period for the ULR phosphorous checker. Mix for 2 minutes, let sit for 3 then test.

The alk, as you said, is instantaneous.

I agree with making sure that you're using each test kit correctly. That difference is large enough to be an issue. I'm not sure which result is more accurate. If checking the video and instructions carefully doesn't clear up the issue, you might need to get a third opinion.

Thanks. I'll be rechecking my techniques.

I primarily use the Hanna checker and periodically cross check, mainly if I get a reading that I question, with my Salifert kit. They are usually within .1 or .2 two of each other and when there was a big variance between the two I retested with the Hanna and it was within .1. Operator error.

I trust the Hanna to be about as accurate as you can get with hobby grade equipment.

I prefer salifert. It used to come with a ref check. Hanna is to flimsy based on how u preform the test

Update!
 

After checking my technique and springing for a LaMotte test kit, I am getting the following readings:

Hanna Checker: 8.9 dKH
LaMotte: 10.64 dKH
Red Sea: 10 dKH

These readings would seem to be within a reasonable margin of error for hobby test kits. If averaged, I get about 9.8 dKH which is just fine. I consider the problem solved and really appreciate the suggestions form the veterans on this thread. Thanks again!:fun2:

I agree that those numbers are close enough for hobbyist kits. I'd consider the problem solved.

I'm not surprised. I got a Hanna checker and tested it against a friends. Using my new and thier 6 month old reagent and the same sample of water pulled from the top middle of the tank we got 4 different results that varied by .9 dKH (~.5 dKH with the same reagent). I think APIs Alk test is far easier and may be more accurate if the sample is doubled then divided by 2 (or trippled then divided by 3)

I use API with a 1ml syringe and multiply reagent used by 26.4 confirmed by a NSW standard. I find this to be ''good enough'' and very inexpensive.