Hanna dkh checker reliable?...

[Greatreefer]

Who here uses hanna dkh checkers? Im having some weird issues with mine and have crossed checked it with two other test kits (red sea) and i think nyos. Took water sample to LFS and both tests came out with a dkh of about 9 where as when i run a sample though the hanna that same sample come out at 6.8. (Reagients exp in 2020)
Just ran another test yesterday, with a brand new unit on both the ato, and a new batch of tropicmarin salt mix. The ato came out at 10, which makes sense because i add BRS soda ash to the top off water. My fresh batch of salt mix came out at 7.1 specks for this particular salt should be around 8.0. I then went to check the tank water again, and it is at 6.8 and all corals look healthy, im thinking it has somthing to do with the hanna checker its self but after purchasing a new unit, and getting basically the same 6.8 crom both the new and older model of hanna checkers, im not sure where to turn.
Has anyone ever had this issue before?
Prior to this issue, ive been using the hanna dkh checker for the last year and a half and have zero issues up to this point.
Ideas?..

 

[motortrendz]

How old is the unit? I had an older one that read on ppm, and after 7 years if failed. Reading low as well. I bought the new dkh readout and it's been on point for a year so far... not sure if there's a way to clean the lens? Or maybe you just have a bad batch of the resolution solution.

I've been getting Pretty good at ball parking the reading just by looking at the liquid when I pour It in the vial. It's a "fun" game i play. Guess the dkh before you press C2..

 

[CindyKz]

I've been getting Pretty good at ball parking the reading just by looking at the liquid when I pour It in the vial. It's a "fun" game i play. Guess the dkh before you press C2..

LOL I'm glad I'm not alone

 

[TK_KW]

I've currently never had a problem with mine. In my opinion Hanna makes the best testing equipment. My .02

 

[BCSreef]

I have been cross checking mine against ATI results (6 times) and the differences are only a few percent. On the other hand, the calcium checker runs about 10% low compared to ATI results.

 

[AdamNC]

I’ve cross checked mine with my Red Sea Pro kit and it’s near dead accurate for me. Maybe off .1-.2 but that could be my interpretation of the liquid.

 

[Dkeller_nc]

Who here uses hanna dkh checkers? Im having some weird issues with mine and have crossed checked it with two other test kits (red sea) and i think nyos. Took water sample to LFS and both tests came out with a dkh of about 9 where as when i run a sample though the hanna that same sample come out at 6.8. (Reagients exp in 2020)

Ideas?..

I don't have the Hanna, so I can't comment about the unit's reliability or unit-to-unit variation. But it might be helpful to know that "drop type" dKH assays are often over-titrated by the user well past the true end-point. That leads to a overly high estimation of the alkalinity in a test sample, and potentially would explain the observations you've made about the discrepancy between your Hanna and the LFS results.

Also, in the case of the Hanna, it may benefit you to use a syringe to measure the water volume into the vial rather than lining up the meniscus of the water sample with the mark. Speaking of which, I'll repeat something about measuring liquids in glassware just in case you're not already aware of it - it's important to line up the bottom of the "curved" surface of the liquid with the marked graduation on the glassware. This page has decent diagram that explains where to measure the water-liquid interface in glassware.

Finally, the only really accurate way to back-check a colorimetric alkalinity assay, whether one-and-done like the Hanna or a drop-type titration with a color indicator is with a pH-based titration with a standardized acid solution. Here's an article by Randy Holmes Farley that describes the equipment you'd need and the procedure.

A pH-based titration with a standardized acid solution would yield a no ifs-ands-or-butts correct value for the alkalinity of a sample assuming that volumes are accurately measured and the pH meter is functional and correctly calibrated. However, you could also make a weakly alkaline solution in RODI with sodium carbonate to back-check the Hanna and/or other titration tests if you have an accurate scale and accurate ways of making the solution. Specifically, a solution of 315 milligrams of sodium carbonate in 1 liter of water should yield a solution with an alkalinity of about 10 dKH. In order for that solution to be accurate, you'll need to ensure that you're using 100% sodium carbonate. Since sodium carbonate absorbs water from the air and converts to sodium bicarbonate over time, you may wish to bake a small portion of your sodium carbonate in the oven to make a solution like this to ensure that it hasn't absorbed water since you purchased it.

 

[Reefer125g]

How do the glass tubes look if they are stained or dirty this will affect the test . Also make sure the outside of the tube is clean free from fingerprints during testing.