Water Test Salifert vs. Greg Hiller's kits

[Dave]

Had my water tested at the meeting yesterday, thanks Josh! I then came home and tested the same sample with my Salifert kits. All of my Salifert results were significantly different.

Salifert -------------------Club test results
Mg 1320 -------------------1195
Ca 430 --------------------380
Alk 3.09 meq/l--------------1.68 meq/l

I could not believe the difference in the kits for the alkalinity. I thought that test was the simplest of the 3 and should be the most accurate.
Thanks again for providing this service to the club. It is a great opportunity to base line your test kits.

 

[Glass Ocean]

Do we know which one is most accurate and how do we know it?

 

[~Flighty~]

This is the first meeting we have had the test kit in use. I think at least 5 tanks were tested, so there should have been enough tests to notice if there was a problem, but maybe you should get a third test just to confirm. (don't know if the tests were done twice at the meeting or anything)

 

[Rays]

All of my Salifert results were significantly different.

Ditto here! I test almost every day, plus I even got a new alk test kit in the mail when I got home. There was a huge difference between the Salifert tests and Greg's.

 

[smcnally]

What tests were used at the meeting? I assumed the tests Greg mentioned that would be available at the meetings were done with a photometer.

 

[Dave]

This is the first meeting we have had the test kit in use. I think at least 5 tanks were tested, so there should have been enough tests to notice if there was a problem.

Josh told me that everyone tested had low alkalinity.

What tests were used at the meeting? I assumed the tests Greg mentioned that would be available at the meetings were done with a photometer.

All the test were titration tests. The kits are from HACH.

>Salinity (refractometer calibrated properly with refractometer salinity standard)
Alkalinity (standard titration with pH indicator)
Calcium (modified HACH test kit, resolution to about 15 ppm Ca)
Magnesium (modified HACH test kit, resolution to about 50 ppm Mg)<

 

[MichaelJ]

I think we need to find an outcome here... if the tests are signifacantly different.. I don't want to have to test with 3 different kits everytime I test.

 

[Joedes3]

Yesterday, my tests were low for alklinity also.

 

[Dave]

Yesterday, my tests were low for alklinity also.

Can you test at home and see what the difference is?

 

[Greg Hiller]

I was also surprised with the low numbers. FWIW, I tested a sample of my water out of one of my frag bags and it came up at 2.2 meq/l. This is also low, but I knew my tank had been running a bit low, but still in a 'safe' range. I prefer to see numbers in the 2.5-4 meq/l range.

I originally 'calibrated' the club's homemade alkalinity kit to the Aquarium Systems Fastest kit.

So, this morning I checked the numbers from my tank again. Using the club's kit I get 2.5 meq/l (I'd cranked up the CO2 on my reactor a bit). I tested the sample with double the normal volume of test water in the Fastest kit (this increases the accuracy of the kit) and also got 2.5 meq/l with the Fastest kit.

I don't know much about the Salifert kit, but I'm surprised that there would be a problems with any of these kits as the test is extremely simple. It's just a pH indicator (dye) with some water and acid tossed in.

There ought to be a way to make a 'standard' for alkalinity that could be whipped up in the lab to be used to test any kit's accuracy (probably a bit of NaCl with some bicarb in it would do the trick). I'll look into it, try to prep it, and make certain that the club's kit's calculations are correct. Until then I'd seriously consider adding some baking soda to the tanks where we saw low numbers. Even if they were at 2.5 meq/l, raising to 3.5 would not (IMO/IME) be a bad thing at all.

I'm curious also, the people that were getting low alk numbers with the club's kit. Are you having problems with the growth of corals?

 

[Rays]

My sps are growing fine.
Club test kit tested alk 1.53 meq.
4.3 dkh

Using two different Saliferts I got 3.09 meq
8.6 dkh
That's quite a disparity.

 

[Greg Hiller]

From Randy's article back in 2002:

http://www.advancedaquarist.com/issues/feb2002/chemistry.htm

The various units used for alkalinity are themselves cause for confusion. The clearest unit, and that used by most scientists is milliequivalents per L (meq/L). For a 1 millimolar solution of bicarbonate, the alkalinity is 1 meq/L. Since carbonate takes up two protons for each molecule of carbonate, it "counts" twice, and a 1 millimolar solution of carbonate has an alkalinity of 2 meq/L.
I'll whip some up in the lab and double check the results. We'll check the kit on a regular basis to make sure we are getting good results.

 

[Greg Hiller]

Okay, my aplogies. I decided to go back to first principles here to get some good numbers.

One of the annoying things about alkalinity test kits is that sometimes the end point is not that clear. To get around that problem, I whipped up some 0.1 N Hydrochloric acid and used it with a Pinpoint pH probe. In salt water the alkalinity can be read at a pH of 4.2, meaning you keep adding acid (titrant) until you see that pH. My pH probe was reasonably well calibrated, but I didn't have a pH 4.0 standard at home. Anyhow, when I tested my tank using this method I got about 4.8 meq/l. Quite high, but apparently not a problem since things are growing pretty well! I think the high alk in my tank must help to deal with the low pH that I typically have (usually below 8.0).

I also used Randy's definition above to check whether I was getting good numbers. I took a liter of tank water, and added 12 ml of 250 mM sodium bicarbonate to it. That addition should have increased the alkalinity 3 meq/l from 4.8 to about 7.8. Sure enough, I needed to add about another 3 ml of the 0.1 N Hydrochloric.

I think the best way to be certain we have a good test kit for the club will be to invest in a pH probe (Pinpoint probably), and use 0.1 N acid to do the titration to 4.2 pH. This will give a very accurate and reproducible number.

Sorry for the growing pains on this folks. It sounds like most people were correct in that their alkalinity was just about twice what we were giving for a number.

FWIW, I have no reason to doubt the rest of the tests that were performed as they were completely separate tests.

So, I think that in the future we will use a well calibrated pH probe, and titrate to pH 4.2 using 0.1 N hydrochloric acid. This does mean that we will need larger tank water samples to do all the tests, but I doubt that is a big deal. It'll probably be better to have 150 ml or so of sample water to run all the tests in the future.

 

[Greg Hiller]

FWIW, I think the original problem with the numbers was the fact that in the test kit that I used to 'calibrate' the club's kit (the old Fastest) the reagent might have evaporated to some extent, concentrating the acid in it.

 

[Aquaman_68]

Jeremy at CRA has a new test kit from the company who makes the tanks he distributes I beleive. I brought a water sample & my results (with salifert kits)to see the difference about a month in a half ago. They were off.....But who's is right? I might send samples out to a lab & then test with some new hach kits I'm going to order to see how accurate they are to lab results...I'm tired of wondering. (I have been for at least three years now since salifert changed their Ca formula in their kits.)
Anyone want to jump in on the lab work? Maybe get samples next meeting & then ship them all together. If I get enough people interested he will give me a break on the testing fee.
LMK,
B

 

[MAReefer1]

I might send samples out to a lab & then test with some new hach kits I'm going to order to see how accurate they are to lab results...I'm tired of wondering. (I have been for at least three years now since salifert changed their Ca formula in their kits.)
Anyone want to jump in on the lab work?
LMK,
B

I can do them at my school, just get me some water samples and I will do it. Im pretty shure my chemistry teacher will have no problem with it.

 

[MichaelJ]

Jeremy at CRA has a new test kit from the company who makes the tanks he distributes I beleive. I brought a water sample & my results (with salifert kits)to see the difference about a month in a half ago. They were off.....But who's is right? I might send samples out to a lab & then test with some new hach kits I'm going to order to see how accurate they are to lab results...I'm tired of wondering. (I have been for at least three years now since salifert changed their Ca formula in their kits.)
Anyone want to jump in on the lab work? Maybe get samples next meeting & then ship them all together. If I get enough people interested he will give me a break on the testing fee.
LMK,
B

I'll jump in on that Brian. I don't want to be wondering for 3 minutes not to mention 3 yrs.

 

[Reef55]

Greg,
Is there a place that shows how to make the 0.1N Hydrochloric acid, and what volume of titration = what meq/l?

Thanks, Mark