Hanna vs. Salifert -- BIG DIFFERENCE

dsinsocal · Mar 6, 2019

Hi All.
I've been running Salifert tests for pretty much everything since I got back into the hobby 2 years ago.

For a long time I was "in tune" with my tank. I was testing at least once a week for the standard stuff and I would get results that "made sense" to me, and adjust dosages accordingly. But about 8 months ago I started seeing some really weird results that I couldn't account for: Magnesium use halted, calcium being consumed faster than I could put it in the tank, suddenly being depleted 3 times the rate as Alk. My Calcium and Alk usage had always been very consistent with each other up to that point.

All of these changes were rather sudden so I questioned whether this was natural (my corals were getting a lot bigger, after all, so a change in consumption patterns was to be expected), or whether I was having a problem with my test kit (the changes in the rates of usage were so sudden that it didn't seem natural). I had my water tested at the LFS, and got a different result -- but I watched them do the test and, let's just say they were less than precise in their procedures, so I couldn't really take their results seriously either.

All this leads up to today. About two months ago I decided to upgrade my technology and invested in a couple of Hanna checkers for Calcium and Alk. I had already been using the low-range Phos checker for 2 years without incident so I thought this would be a good way to put my fears to rest.

The baseline test looked accurate and when I increased/decreased dosing by a couple ML over the next month, the results followed suit. Fast forward to yesterday, my Hanna Alk reading was shockingly low -- 7.5 -- after hovering between 9 and 10 since I started testing with it. I tested again and it was 8.1. Then again, using the other cuvette from the kit and it was 8.3.

Before people ask, I rinse my cuvettes with RO water, I turn them the same direction in the tester each time, I wipe with microfiber towel before each test, etc.

The swing from 7.5 to 8.3 is concerning enough, as that is just way too much variance to be considered acceptable. Worse yet, when I decided to compare results to *a freshly opened Salifert kit*, I received readings of 12.1 !!! Surely there must be a mistake, I concluded, so I ran the test again and got the same exact result: 12.1.

Which freaking test do I believe? They are both at extreme ends of acceptable ranges so I don't want to make any dosing decisions based on either of them.

Dkeller_nc · Mar 6, 2019

Personally, I'd be inclined to believe the Salifert because it's an actual titration based on the method in Standard Methods for the Examination of Water and Wastewater (the bible when it comes to water testing). Unless Salifert really screwed up and the acid reagent provided with the kit (the one you put in the syringe) is way off, there's not a whole lot to go wrong. If you want a no-ifs-ands-or-buts answer, and you have or are willing to purchase the equipment, you can do a titration with a buret, stir plate, pH meter, and a 0.1N HCl standardized acid solution. The only absolute requirements is a way to accurately measure the volume of the sample, the volume of the acid added to the sample, the standardized acid, and the pH meter. The stir plate and buret are optional items that make the procedure a lot easier.

JimWelsh · Mar 6, 2019

Make sure you aren't seriously overshooting the Salifert endpoint color: https://www.reef2reef.com/threads/alkalinity-titration-endpoint-ph-salifert-endpoint-color.543556/

Dkeller_nc · Mar 6, 2019

That was an excellent study, and very well done. One thing to recognize, and that Jim mentioned at the bottom of the post, is that if you overshoot to the orange-pink color, you're about 5% - 10% too high. That's what my own experience tells me - I checked the pH of the Salifert "completed" titrations via a quick 'n dirty pH probe measurement and came to the same conclusion. That said, 5%-10% too high doesn't come close to explaining the Hanna/Salifert discrepancy you've noted.

S-t-r-e-t-c-h · Mar 6, 2019

Keep in mind that reagents expire too. I'd trust the freshly opened kit over one that has been open for a while...

Duffer · Mar 6, 2019

I know what you are going thru as it happen to me and i was going out of my freakin mind. After doing a little research i did the following and now hanna is in line with my salifert.

I use a syringe to get 10 ml of tank water, what i found out was the line on the tube for hanna was not true 10ml. I also when i put the hanna tester away i leave the cap off. These both things plus what you are doing seems to help get the results in line.

Terry Brown · Mar 6, 2019

I have had problems with the consistency of the reagents from bottle to bottle of the Hannah Alk. I posted this question on another thread a few months back. It appears other reefers are having problems with the consistency of Hannah Alk between lot numbers.

I now always do a test side by side of Alk, comparing the new bottle to the old bottle of reagent.

Here is the thread.
https://www.reef2reef.com/threads/hannah-alkalinity-refill-inaccurate.489630/

toybox22 · Mar 6, 2019

duffer said:
I use a syringe to get 10 ml of tank water, what i found out was the line on the tube for hanna was not true 10ml. I also when i put the hanna tester away i leave the cap off. These both things plus what you are doing seems to help get the results in line.

I've found this to be true as well. I started using a 10ml micropipette and almost none of the lines actually match up. Each vial is different for me. Not by a huge amount, but I'd imagine it's enough to skew my results if I didn't use the same vial each time.