Accuracy of test kits and AWT

[treehugger]

So i've been pulling my hair out over some conflicting results from various test kits. I've purchased salifert, LaMotte, Elos, and sent samples to Aquarium water testing to compare accuracy. I've noticed that salifert, elos and Lamotte tested against the Salifert check solution and the results from A.W.T. vary greatly (to the tune of 3dkh). Elos tested the lowest always, Salifert and LaMotte were close (salifert being on the high end) and AWT put the results on the lower end of the middle tested by all three test kits. As I take care of 18 aquariums full time, accuracy in testing for dosing purposes is very important. Any suggestions on what kits are typically the most consistent and what is the best way to make sure a kit does not lose credibility over time once the reagents are opened. Also how much faith should I put in Aquarium Water Testing's results?

 

[NWDiver]

Great question.
I'm riding along to see what folk have to say...

 

[ac7av]

Tagging along too.
I’ve always thought the consumer grade junk we buy is good enough to get you in the ball park and for most people that good enough. I can see your concerns on that, accuracy is your business and you have to have it right.

 

[Red C Aquarium]

home slice
whats up !

I have tested elos to be lower than sal also , i dont like any of these myself.

I did like the old aquarium system alk before it was dropped .

I find the best results with the seachem alk , the problem is they only give you a tiny ass little bottle.and it only comes w/ a ph kit.

ARSA

 

[eww]

I'm tagging along too. We are in the market for these and I refuse to buy junk from Pet Smart or Petco. I am just looking for a starter set myself.

 

[treehugger]

I've basically tried at least 6 brands in the last month and they are all significantly off from what the lab tested. I took all water samples from the test aquarium at the same time so there would be consistency in the samples. I tested with each test kit twice and even found that there was some differences from test to test. I attribute this to varying measurements in the powdered reagents (CA and MG). I like the LaMotte because the powdered reagents are in pill form so they seem to be pretty uniform. I've even busted out a scale that weighs to the hundredth of a gram to weigh the powders for consistency. The powders also appear to absorb moisture from the air just from being opened and closed a couple of times. I strive for accuracy and consistency and have yet to find a company that provides both. I wish that more of the test kits came with test solutions so I could at least see if they are consistently off so I can correct for that after testing. I've actually raised both the alk and ca in most tanks a bit so that if they are off at least they fall closer to where I like to keep my levels 9.5dkh/430CA/1350-1400 MG.
ps...i'm also looking for a good boron and strontium test kit...maybe I should just build a lab...haha

 

[treehugger]

So I just received my second set of results from A.W.T. to compare to the samples that I took at the same time as the AWT samples that were sent in. Given the claims of AWT for accuracy, I am taking their results at the closest to actual values in the tank (although I have read of issues with their testing methods-comments by Boomer). I used Elos, Salifert, and LaMotte test kits to test the water. Here are the results that I recieved.
AlK: AWT 6.5 Salifert 9.0 Elos 7.0-7.5 (two different kits) LaMotte 7.7dkh
CA: AWT 331 Salifert 425, 430 Elos 410 LaMotte 460
MG: AWT 1750 Salifert 1410 Elos 1200 and 1350 (two different kits)

As you can see the values vary greatly across the board. If I use the Lamotte Alk test with 4ml of tank water instead of the 5ml it shows the Alk=6.5dkh. Obviously this holds little value as it is not the recommended concentrations for the titration but I thought it was interesting to mention. The magnesium and alk are extremely troubling to me as there was as much as 550ppm difference in the test kits. As for the Alk it's unacceptable to think that I was keeping my level at 9dkh on purpose and it was really on 6.5. I checked all three test kits against the test solution provide in the Salifert Alk. The results of that are relatively close to what the test solution claimed:
Test Solution: 7.3+/-
Salifert: 7.9
LaMotte 7.1
Elos 6.5

I think the lesson here is that you really can't rely on these test kits for consistency. I was a marine bio major and spent enough time in various labs to feel confident in my ability to perform basic titrations. Having been in the hobby for 10 years and professionally for 3, the coral health tipped me off to wack parameters but I never thought this wack. Sorry for the vent but I'm very frustrated by the whole thing.

 

[treehugger]

I've looked into AWT on other forums as well and have seen that they do have a tendency to show lower CA results because of the form in which they are testing for it and the fact that they use probes which have their own host of problems. This still leaves the Alk and MG in ranges that are far different from the home test kits. I guess the next step is to figure out a way of making or buying a test solution that I can use to calibrate my home test kits...food for thought.

 

[Boomer]

I do ot buy in to AWT results still and most other chemist don't either. The reason behind their low Ca++ is they do not know what they are doing and using an ISE probe, where they do not know what they are doing and the same for Mg++.


So, why does a Salifert Alk read higher than the rest ? It is suppose to All of these other kits are FW Alk kit and DO NOT test to a lower end point needed for seawater. So, they read about 10 % lower than they should. Or ~ take your Alk kit reading, if NOT a Salifert and add 10 % to it.

MG: AWT 1750

This is just so funny, not worthy of a comment.

For me, Salifert for Alk and Elos for the rest.

Lastly, DO NOT forget about accuracy that all these kits have i.e., +/- x % and then there is user error. One can expect Ca++ to be +/- 20 ppm and Mg++ to be +/- 50 ppm or so. A titration drop test may be off 1 drop / 10 -20 drops. So, that is ~5- 10% of reading maybe. More than likely 5% for those we use. So, for Mg++ +/- 5 % for say 1300 is +/- 65 ppm

 

[returnofsid]

Boomer, if I'm understanding this correctly, Salifert Alk test kit is meant for saltwater, while the rest are meant for freshwater? Is this true of other parameter test kits, such as Ca and Mg, as well?

 

[Boomer]

Yes . FW Alk kits do not titrate a low enough pH to show AlK for seawater. FW kits titrate to a pH of 4.5 pH and seawater needs to go down to 4.2 pH. So, when the kit only titrates to 4.5 pH you loose ~ 10 % of the Alk reading. Ca++ and Mg++ are much, much less affected by seawater in kits. But meters for Ca++ and Mg++ is a whole different ball game when dealing with Seawater.

From Randy, "What is Alkalinity"

The precise endpoint of a total alkalinity titration isn't always the same pH, but rather depends a bit on the nature of the sample (both its ionic strength and its alkalinity). For normal seawater, this endpoint is about pH = 4.2. In freshwater it depends strongly on the alkalinity, with an endpoint of pH = 4.5 for an alkalinity of 2.2 meq/L, and pH = 5.2 for an alkalinity of 0.1 meq/L.

 

[FreakinReefin]

I'm having a lot of issues with my test kits as well. Especially with dKh. I have a API, Elos, SeaChem and now Salifert. I have only tested with the API and Elos and am getting a HUGE difference. My API is telling me that the dKh is like 6 and my Elos is saying 13-14! I had forgot about the SeaChem until earlier today, so I will test when I get home and I just purchased the Salifert today...so I'll see what that turns out to be.

Any idea why the API and Elos would be so different??

 

[NWDiver]

I have an api that is only a few months old, I will compare it to my elos and salifert to see what I get tonight...

 

[FreakinReefin]

I have an api that is only a few months old, I will compare it to my elos and salifert to see what I get tonight...

Are you stalking my posts??:lol: That would be awesome if tested and compared. It's super bizarre and I am getting very frustrated.

One thing I am doing different is filling the API test tube with exactly 5ml of water. Now the API test utbe has a line on it and stated that the line indicated 5ml, however it's quite far off. I use the syringe and the test tube0 from the Elos kit for both the API and the Elos tests.

 

[NWDiver]

Yep, that's me post stalker!
I noticed that nearly all the kits tubes are far from accurate!
I used a syringe to measure the water.
So here is what I get two tests each all in DKH.
Brand new Salifert (opened today) #1=8.6 #2=9
Notes: My kit is off of the cal solution considerably I ran all of the cal solution in three tests It should have read 7.4 I got 8, 8.3, 8.3
My dye bottle gives me no confidence that it is a very measured drop.

New Elos: 7, 7 Really hard to see the change, very subtle perhaps 7.5

9 month old Sera Marin: 7 I really like everything about this kit! No idea if it is accurate

Two month old API: 8, 8 easy to read!

Yes, my alk is low
FWIW

-Todd

 

[psb]

I wonder if there are other brands of test and if there are any experienced reefers that swear by not swear at certain tests. I am starting to believe in the idea of testing my fresh mixed saltwater and based on how my tank uses it and adjusting my wc to keep parameters the same on an ongoing basis, because of the frustration with tests.