DIY Alkalinity Test

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I got an email from R2R regarding a DIY alkalinity test. All you need is a pH meter and hydrochloric or sulfuric acid. I dug out my pH meter that I haven't used since I installed my controllers. I figured that as long as it has been setting up that the battery had leaked and probably ruined it but when I flipped the switch it came on! I had put a label on it when I last calibrated it in 2011 so that tells you how long it had been sitting. I ordered a bottle of acid just now and when I get it I'll compare the reading to the Salifert test.

In case some of you didn't get the email, here's a link:
A DIY Alkalinity Test: By Randy Holmes-Farley - REEFEDITION
 
Orphek OR3 reef aquarium LED bar
My lab grade pH meter needs a replacement probe every 12 to 18 months, which cost more than 20 dollars. It's cheaper for me to just buy an alkalinity test kit. If you are color blind, it may be easier to use a pH meter rather than a bromophenol blue or a bromothymol blue solution.
 
I buy the eBay probes from China. They cost about $8 - $9 with shipping. I buy them 3 at a time to save on the shipping. They're not "lab grade" (I don't think) but they work fine for me.
 
Deltec
My hand held pH meter needs a specific one unfortunately. I don't know if it is any cheaper to test alkalinity with a pH meter since you need to add calibration fluid cost to the total as well. However, it would be a lot more accurate than some hobby grade test kits sold by local pet shops. I saw three of them reading wildly different values when testing the same water...
 
H@rry said:
I got an email from R2R regarding a DIY alkalinity test. All you need is a pH meter and hydrochloric or sulfuric acid. I dug out my pH meter that I haven't used since I installed my controllers. I figured that as long as it has been setting up that the battery had leaked and probably ruined it but when I flipped the switch it came on! I had put a label on it when I last calibrated it in 2011 so that tells you how long it had been sitting. I ordered a bottle of acid just now and when I get it I'll compare the reading to the Salifert test.

In case some of you didn't get the email, here's a link:
A DIY Alkalinity Test: By Randy Holmes-Farley - REEFEDITION
Click to expand...
Nice! I want to try this. If it works well I won't have to bug my wife every time I want to test the water (colors can be an issue for me).
 
Nutramar Foods
Yeah, I like that too. I want to be able to read a number. I don't want to trust my guessing whether it's still a little bit purple or maybe it has turned orange.
 
www.dinkinsaquaticgardens.com
Be careful with the acid. Concentrated HCl will fume and burn your nose if you aren't careful. I always hold my breath when working with it. Eye protection isn't a bad idea
 
I wonder how much different the acid is from whatever is used in a Salifert test kit. Sounds like the procedure is very similar.
 
H@rry said:
I wonder how much different the acid is from whatever is used in a Salifert test kit. Sounds like the procedure is very similar.
Click to expand...
Well Randy's protocol says to use 0.1 N acid which is fairly dilute compared to the concentrated HCl one might buy. I guess you could buy it at 0.1 N, but I prefer to make it to 0.1 N as I have it on hand at 12.1 N.

What kind of acid and what concentration did you buy Harry? I bet the kits use it around 0.1 N
 
Last edited:
Ecoscape Reef Rock
Tested

OK, I got around to doing the test this afternoon. Here's the results:

Started out with a Salifert test kit - expires 7/19. It showed 9.7 alk

Calibrated my pH meter with 4.01 and 7.01 solution.

Got a new bottle of .1 N Hydrochloric acid.

Used a Pyrex 1 cup measuring cup. Filled it to the 1 cup line as close as I could.
The pH in the tank water measured 8.35. I question that as I'm running a calcium reactor which usually drops the pH to around 7.7 or 7.8. One explanation is that the meter was calibrated with 4.01 and 7.01 solution as opposed to 7.01 and 10.01 which I would normally use. This put the actual pH out of range of the calibration fluids but I though that it would make it more accurate at the target pH of 4.5 that I would be shooting for.
I used a 5 ml syringe from an old test kit. Dumped the whole syringe in to start with as I could see from the chart that it would take more than that. I refilled the syringe and started adding .1 ml at a time while I was stirring with a spoon. I got to 6.9 ml total and the pH was reading 5.? (I forgot the number and didn't write it down because I didn't think it was significant at the time). I added another .05 ml which brought the pH down to 4.39. I was not expecting it to change that much so quickly. You would almost need an dropper at that point to get it right at 4.5 pH.

From my calculated extrapolations that would put the alk at 8.1.

The explanations for these findings are:

1. At least one of the methods are inaccurate.
2. I didn't measure the cup of water accurately. (looked good to me)
3. The pH meter was inaccurate.
4. The spoon was affecting the pH.
5. I incorrectly interpreted the change from purple to orange on the Salifert test.

My guess would be item 5 above. Anybody got any comments?
 
Last edited:
Nutramar Foods
Like you I struggle with color change and color comparisons. Every time I test my water with the test kits I can afford I really miss the equipment I used when working that returned an actual value instead of pretty color.
 
I posted my findings in the main discussion thread as well. The opinions put forth was that the Pyrex measuring cup that I used was not accurate or that I misread the Salifert colors. I doubt that the cup was inaccurate enough to produce the difference that I found. I now really believe that I have been going a little too far with dropping the reagent into Salifert test. I never was really too sure I had done it correctly. Looks like my alk never was quite as high as I thought it was. This is good to know.
 
I think that if an exact volume was required the unit would not be cup. ??
 
www.dinkinsaquaticgardens.com
TrishW said:
I think that if an exact volume was required the unit would not be cup. ??
Click to expand...

There are 5 volumes on the chart but a cup was the only one that I had. I could have used 250 ml but I would have had to make multiple squirts with a 5 ml syringe and I'd probably lose count somewhere in the process. I may order a graduated cylinder.
 
H@rry said:
I could have used 250 ml but I would have had to make multiple squirts with a 5 ml syringe
Click to expand...

That would be a lot of squirts to have to count!

H@rry said:
I may order a graduated cylinder.
Click to expand...

I bet this would be one of those items that once you had it you would wonder how you ever lived without it. Now I am sitting here wondering how often I would use a graduated cylinder :)
 

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