Testing ALK testing accuracy

[IPT]

I've read that the HANNA tester reagent can drift over time. I also just got a ReefKeeper KH tester (plus). Testing with consistent values is nice, but if I get a drift is it the tank or the reagent? What I would like to know is if (and I am sure there is) a way to make (or buy?) a standardized seawater solution of a known ALK level so I can test the accuracy or +/- values of the test reagents.

 

[Garf]

I've read that the HANNA tester reagent can drift over time. I also just got a ReefKeeper KH tester (plus). Testing with consistent values is nice, but if I get a drift is it the tank or the reagent? What I would like to know is if (and I am sure there is) a way to make (or buy?) a standardized seawater solution of a known ALK level so I can test the accuracy or +/- values of the test reagents.

Depends how much effort you want to put in;

A DIY Alkalinity Test: By Randy Holmes-Farley - REEFEDITION

Alkalinity is one of the most important measurements that a reef aquarist can make. It can become rapidly depleted in many aquaria, requiring frequent measurement in order to maintain stable levels.

www.reefedition.com

 

[IPT]

Depends how much effort you want to put in;

A DIY Alkalinity Test: By Randy Holmes-Farley - REEFEDITION

Alkalinity is one of the most important measurements that a reef aquarist can make. It can become rapidly depleted in many aquaria, requiring frequent measurement in order to maintain stable levels.

www.reefedition.com

Man, that is interesting. Well I guess now I understand how the KH Keeper works . It has a PH probe and it adds a reagent (I would now assume some sort of acid) to "somehow" determine the Alk. I guess it adds reagent to the sample until the PH is 4.5 and that would do it. No wonder it calibrates the PH probe with 7.00 and 4.00 fluid.

Thanks for the link. Looks like unless you can measure the Acid in fractions of ml's, it makes a pretty big jump (over 1dKH from adding 1ml). Guess I was looking for something simple like the solution they have for refractometers with a known value you could just test. Add the fluid of a know dKH, do your test, and determine the margin of error.

 

[Garf]

Man, that is interesting. Well I guess now I understand how the KH Keeper works . It has a PH probe and it adds a reagent (I would now assume some sort of acid) to "somehow" determine the Alk. I guess it adds reagent to the sample until the PH is 4.5 and that would do it. No wonder it calibrates the PH probe with 7.00 and 4.00 fluid.

Thanks for the link. Guess I was looking for something simple like the solution they have for refractometers with a known value you could just test.

I use the salifert for what it's worth. Appears reliable. No idea how reliable the automated testers are. Probably work great, until they don't.

 

[RelaxingWithTheReef]

I have seen this subject come up many times, so I thought I would share how I addressed the issue. Maybe Randy can confirm that I didn’t make any amateurish errors.

Creating an Alkalinity Standard:
I created an 8.0 dKH (142.88mg/L) alkalinity standard using Biopharm Alkalinity Standard 1000 ppm. Using a class-A graduated pipette with tolerance ±0.1mL, add exactly 14.3 ml of the 1000 ppm standard to a 100 mL volumetric flask. Fill balance of 100 mL with DI or distilled water. Mix, and you are all set. All this stuff is available on Amazon.

I am not 100% sure, but after some comparison testing including the “Fauna Marin Multi Reference”, it appears this standard reads as 7.8 dKH on the Hanna HI772. In any case, I use this as MY Hanna 7.8 dKH standard, and I am certainly not too concerned if the absolute value is off a couple tenths.

Hanna Drift:
I can confirm the Hanna alkalinity reagent drifts. Aging in a sealed bottle does not appear to cause drift. Opening and closing the bottle 20 times over a period of time appears to degrade the reagent, and cause significant drift as the reagent is consumed. When you open a new bottle, you can sometimes see a big jump in the alkalinity reading.

When I open a new reagent bottle, the first thing I do is transfer the reagent to three 10mL glass bottles (from Amazon), topping them off to minimize the air, and storing them in a dark place. This appears to eliminate the drift.

Calibrating the Hanna test:
I typically purchase 10 alkalinity reagents at a time directly from Hanna, and hopefully they are all the same lot number. I calibrate the batch with the 7.8 dKH standard, and make an adjustment typically from -0.2 dKH to +0.2 dKH. I have never received a reagent bottle outside their stated test kit accuracy of +-0.3 dKH, so I think I’m on the right road. Bottle to bottle accuracy within the same batch number appears to be excellent, so I only calibrate once for the batch.

This procedure appears to produce repeatable alkalinity testing, without drift. I also have to say that for its simplicity, accuracy, and cost the Salifert test is very impressive.

 

[IPT]

I have seen this subject come up many times, so I thought I would share how I addressed the issue. Maybe Randy can confirm that I didn’t make any amateurish errors.

Creating an Alkalinity Standard:
I created an 8.0 dKH (142.88mg/L) alkalinity standard using Biopharm Alkalinity Standard 1000 ppm. Using a class-A graduated pipette with tolerance ±0.1mL, add exactly 14.3 ml of the 1000 ppm standard to a 100 mL volumetric flask. Fill balance of 100 mL with DI or distilled water. Mix, and you are all set. All this stuff is available on Amazon.

I am not 100% sure, but after some comparison testing including the “Fauna Marin Multi Reference”, it appears this standard reads as 7.8 dKH on the Hanna HI772. In any case, I use this as MY Hanna 7.8 dKH standard, and I am certainly not too concerned if the absolute value is off a couple tenths.

Hanna Drift:
I can confirm the Hanna alkalinity reagent drifts. Aging in a sealed bottle does not appear to cause drift. Opening and closing the bottle 20 times over a period of time appears to degrade the reagent, and cause significant drift as the reagent is consumed. When you open a new bottle, you can sometimes see a big jump in the alkalinity reading.

When I open a new reagent bottle, the first thing I do is transfer the reagent to three 10mL glass bottles (from Amazon), topping them off to minimize the air, and storing them in a dark place. This appears to eliminate the drift.

Calibrating the Hanna test:
I typically purchase 10 alkalinity reagents at a time directly from Hanna, and hopefully they are all the same lot number. I calibrate the batch with the 7.8 dKH standard, and make an adjustment typically from -0.2 dKH to +0.2 dKH. I have never received a reagent bottle outside their stated test kit accuracy of +-0.3 dKH, so I think I’m on the right road. Bottle to bottle accuracy within the same batch number appears to be excellent, so I only calibrate once for the batch.

This procedure appears to produce repeatable alkalinity testing, without drift. I also have to say that for its simplicity, accuracy, and cost the Salifert test is very impressive.

Awesome, thanks - this sounds like a very good approach and has some simple solutions as well. Appreciate you taking the time to document your process.

Like you and I imagine many of us I don't really care if my ALK is 8.29 or 8.43. What I do care about is my levels stay consistent over time. If I am unknowingly raising my ALK in reality without knowing I am actually overcompensating for a reagent that is giving a lower reading over time that is an issue.

All that said, it would seem to me that the Automated system using the reagent and PH is excellent, but there are so many variables. Are the doses being measured accurately, is the tool (PH ) accurately calibrated. There are a lot of places this can go wrong if not from the get-go certainly over time. Lots of stuff to watch here, bit of course most importantly the health of the tank inhabitants!

 

[taricha]

There's two standard recipes here. Both are easy - sodium carbonate and NaOH.
https://www.reef2reef.com/threads/diy-alkalinity-standard.714738/