The Hanna HI 755 Alkalinity Colorimeter Review

by • October 13, 2010 • Reviews, Test KitsComments (6)6828

As promised, here is my review of the new Hanna HI 755 Checker Alkalinity Colorimeter. This review will cover the unboxing of the HI 755, testing, and comparison with other popular alkalinity test kits (API, Salifert, and LaMotte).

Read the full review (full of pics) after the jump. Feel free to click on each pic for a bigger version.


The HI 755 kit, as I would assume all of the Hanna Checker HC test kits, comes in a sturdy white Hanna plastic case. The case comes with the blue Alkalinity colorimeter gizmo, six sample reagents, and two cuvettes (testing containers), one 1.5v AAA battery, and instructions. The 25-pc reagent pack comes in a box (fyi, my Hanna Phosphate reagents were packed in a small Ziploc bag).  The box is aptly labelled with the expiry date and the batch lot number (more on the lot number later).

You need one AAA battery (included) to power the HI 755. A Phillips screwdriver (not included) is needed to unscrew the bottom.

I wanted to mention two small things I’ve noticed. The cuvette didn’t come with that small extra plastic cap that you use between the cuvette lip and cover (as on what came with the phosphate colorimeter). Also, the reagent has a yellow tint to it and the water turns blue upon mixing — this info might be useful for some curious chemists out there.

Testing Procedure

It’s quite easy to use the HI 755. There are mainly 8 steps:

  1. Fill the cuvette with 10 ml of your tank water.
  2. Press the HI 755 button and wait for display to indicate ‘C1‘.
  3. Insert the cuvette and press the button. Wait for display to indicate ‘C2‘.
  4. Remove and open cuvette, add reagent, close.
  5. Shake for 30 seconds.
  6. Re-insert cuvette, and press and hold button until it starts the 2-minute countdown.
  7. When the display indicates ‘C2‘ again, invert the HI 755 three times to clear micro-bubble build-up on the cuvette.
  8. Press the button and read the results.

There are several things I’ve noticed that have been improved on the HI 755, compared with my HI 713 (phosphate colorimeter). First, Hanna increased the auto shutoff time from 2 mins to 10 minutes. This means you can now take your time adding the reagent, mixing, etc. On the HI 713, you had to make sure to prepare the reagent ahead of time as 2 minutes is a bit too short to open, mix, and shake.

Another improvement is on step 7. It has been added so you get reminded to invert the tester three times to clear the micro-bubbles (which for sure would affect the results) that might have accumulated during step 5. On the HI 713, after the countdown, it immediately displays the reading.

Lastly, another huge advantage of the increased shutoff time is that the result gets displayed for about 10 minutes. You don’t have to worry about the device shutting down before you’ve seen the measurement. Now, it gets shown for quite a long time and you can just press the button to turn the display off.

One enhancement that I wish was added was for the device to beep on every major step. This will let you to at least do concurrent testing of other parameters without being stuck watching the  display.

Testing the Tester

Now for the exciting part. I wanted to test the accuracy of the HI755. This is the time a big batch of different alkalinity calibration solutions but not knowing where to get nor how to make them, I’ve thought of just doing two things — check the consistency of the HI 755, and then compare them with other popular alkalinity test kits. For those wondering, I have several test kits since I’m into two part dosing and I wanted to be precise with my tank’s alkalinity so I can adjust the dosing accordingly.

For the consistency test, my test routine was to fill the cuvette with tank water, test, rinse with tap water, rinse with RO/DI water, and dry the cuvette and cap with paper towel. I made sure to turn off my auto top-off, and dosing pumps on my tank to minimize any alkalinity changes.  To help validate my results (so no one would think that I’m making up numbers), I’ve thought of taking pics of each reading (there is no way to show a certain reading on the display manually).

I performed five consecutive tests which lasted a bit less than an hour. Here are the results (in ppm):

And the results in ppm, meq/L, and dKH (you can use an online tool to easily convert between standards). Note that the difference between the lowest and the highest readings is only ~0.4 dKH.:

Looks all nice and consistent right? Well not so fast. Before performing the five tests I’ve logged above, I thought of first using the sample reagents that came with the kit. I tested three times and my results were 151, 149, and 152 ppm. For some strange reason I thought of getting a reagent from the 25-pc reagent pack box and surprisingly, it shot  up to 169 ppm! I got confused and thought I might have done something wrong. I continued testing, but using reagents from the 25-pc reagent pack. Those are what you see above.

After the tests, I thought of looking at the reagent packettes and see if I can spot a difference. The only apparent difference are the lot numbers labelled on each reagent packette. All the reagents that came free with the kit had Lot 1 and all the ones in the 25-pc pack had Lot 4. The only thing I can think of is there might be a problem with the Lot 1 batch as I knew my tank’s alkalinity is usually about 10 dKH. Anyway, this is the time for you guys who have the kit to verify my findings.

To check the accuracy of the tests, I’ve decided to pull out my three other alkalinity test kits — Aquarium Pharmaceuticals (API), Salifert, and LaMotte (they are all within their expiry dates). Here are the results:

For Salifert and LaMotte users, here’s a pic of the results (left: Salifert, right: LaMotte):

Note that the Salifert result is quite odd since it’s the only high one among the lot. I actually performed several Salifert tests (about 4 times) just to make sure and all ranged from 11.2 to 11.8 dKH.


We are at the mercy of test kits. Often times we look for the easiest ones to use, maybe the cheapest, or the most popular ones. What is common to test kits however, is a lot of the decision is left to the tester. Is it yellow already or is there still a hint of green? Is it pink or still purple? Is the purple turning red already? Am I swirling it correctly? Should I stop? Did I put too much? We face the same dilemma every time we test and it is us who make the final decision.

The HI 755 strays from the guesswork since it provides you with a specific number, and in 1 ppm increments. A change of 1 ppm is only 0.02 meg/L and only 0.056 dKH. The tests I’ve made only show that it’s quite consistent with only ~0.4  dKH difference between the lowest and the highest. I have yet to test it with an alkalinity calibration solution but from the data I have gathered, it is precise enough with the LaMotte, which I regard to be one of the most precise test kit out there. If it is really that precise (I hope others can weigh in on this),  it can be a dream gizmo for two part dosing and calcium reactor fans — just test on a specific time of the day or the week, and you can adjust more precisely your timers, CO2 rate, or effluent rate.

As for the cost, well that’s a different matter as it can be the more expensive test kit out there. The HI 755 is about $50. A 25-pc pack of reagents is about $9 which comes down to about $0.36 per test. It’s even more expensive than LaMotte which is about $0.27 per test.  Salifert is about $0.10 and API even cheaper.

Most of the time however, folks just want to know if their tank’s alkalinity is ‘in range.’ In such case, you don’t really need to be that precise, as test kits like API and Salifert will do the job — cheap and no battery needed.

In any case, this gizmo will be part of my testing arsenal.

I hope you enjoyed this review. Please don’t hesitate to post some feedback below. Thanks.

Note: I am not a chemist by trade so this review was done from a hobbyist’s perspective. If you find a problem with my testing, or if there is a better way for me to present results, let me know and I’ll see how I can improve the review. As an fyi, I purchased all of the test kits I have mentioned in this article and none of them were provided for review/free. It wouldn’t have mattered anyway since I am always objective and honest with my reviews. Reviews (good or bad) let companies keep improving their products. Cheers!

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  • Aiolos

    Hanna HI-755 Alkalinity test
    A way for a double increase of the test while simultaneously reduces its cost to half.
    I believe the image is understandable.
    The steps described in the instructions remain unchanged, except for the quantities of water and reagent which must be reduced to half. (5ml water, 0,5ml reagent).
    Because the cover of the device will remain open after the placement of the plastic tube, it will have to be covered to prevent natural light from coming in.

    • Reggie Suplido

      Ha! Great info! Now we need to look for cuvette that is about half the size so we can close the cover. :)

  • Dennis

    Great Job Reggie take the time to show Us (me) How the hanna checker works, I love mine, and i look forward to the Calcium Checker,, Do you have the phosphate Checker??

    • Spock123456

      I have phosphate checker and works great my phosphate was high (22) but after buying reactor it went to (0). The checker came really handy.

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