4 Different Readings from 4 Alk Tests, Thoughts?

[reefdiculous]

Hey Guys,

Recently, I bought, a test kit for measuring dKH (ALk) and I was wondering if that test kit was accurate. So, I went out and bought another test kit to testing against the first one. Unfortunately, I got different results. So, then I bought another 2 test kits to see which one was inaccurate, but I got different results again!

Needless to say I went down the rabbit hole trying to get accurate numbers.

I was wondering if anyone out there has had similar experiences with these tests kits, and which one out of the 4 is most likely to be correct.

Here were my results... yes I read the directions and repeated each test several times.

Red Sea Pro = 8.4 dKH
API= 8.5? The sample went from blue to green on 8.0. With the next drop it went yellow, so I assume it's 8.5
Salifert Profi = 9.3 dKH
Hanna dKH Checker = 9.6 dKH

[Agostinone]

That's strange. I have the Red Sea Pro and Hannah. I prefer the Hannah because it's easier to use. I get the same answers whenever I compare them. The Red Sea is a little tricky because the end point isn't purple but rather blue so you need to go past the purple to get accurate results. That might explain why the Red Sea is lower than the Hannah in your test.

[thegrun]

Did you check the Salifert test kit against the 6.7 dKh standard solution they include in their test kit?

[scuzy]

Were they all tested against the same tank water art the same time? Alk could differ on different time of days.


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[reefdiculous]

That's strange. I have the Red Sea Pro and Hannah. I prefer the Hannah because it's easier to use. I get the same answers whenever I compare them. The Red Sea is a little tricky because the end point isn't purple but rather blue so you need to go past the purple to get accurate results. That might explain why the Red Sea is lower than the Hannah in your test.

Hmm... that's strange, the instructions say that it goes from blue to red. Well, in my case it actually goes to pale orange (that's the darkest I can get it).

http://www.redseafish.com/wp-content/uploads/2013/11/1775X1197_0002_Alkalinity-TK.jpg.png

[reefdiculous]

Did you check the Salifert test kit against the 6.7 dKh standard solution they include in their test kit?

Nope, I'll have to do that. :)

[disc1]

So you've basically got two that say 8.5 and two that say about 9.5. I bet the alkalinity is somewhere between 8.5 and 9.5 so it's in good shape.

As alkalinity kits age, they tend to start reading low. How old are these kits?

[reefdiculous]

Were they all tested against the same tank water art the same time? Alk could differ on different time of days.


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I tested them all on the same tank at the same time.. well, 5 minutes apart or so. :)

[reefdiculous]

So you've basically got two that say 8.5 and two that say about 9.5. I bet the alkalinity is somewhere between 8.5 and 9.5 so it's in good shape.

As alkalinity kits age, they tend to start reading low. How old are these kits?

I bought them all recently like in the past week. Most of them say they expire in about 2 years from now.

[Agostinone]

Blue to Red on the Red Sea, you're correct, I was thinking about the Ca test--my bad.

My other observations stand.

One thing I do is after I hit what I think is the end point is too keep going to be sure I'm interpreting the color change correctly. I also found that with my eyes I got better results holding white paper behind the vial.

[texdoc77]

All your measurements are basically wrong. It's not you. Our test kits are simple and not commercial grade. They get you in the ballpark. Once you are in the ballpark work on precision, not accuracy. Funny thing about saltwater tanks, precision i.e. stability is more important than any one number. I mean just go read a thread on what the "optimal" parameters are for your type of tank. There is always a range. Ask anyone what is more important a specific number or a stable tank. Choose a kit. Test a LOT. Test the same way, in the same lighting at the same time of day. Anticipate what the number is. If its not what you expect, test again. If it still not what you expect, check your corals/livestock.

IMO it is best to be precise with your measurements and learn the way your fish and coral behave because the dirty little truth is your numbers are wrong. But at least you're in the ballpark...

[Ron Reefman]

Well, what you've done is just proven that there is no best brand of test kit. Whether you have 8.5dKH or 9.5dKH, both are acceptable numbers and your tank is fine.

And to be honest, IMHO, if you expect to get REALLY accurate numbers from an aquarium water test kit, you are kidding yourself. They give you a ballpark and you try to keep it stable.

[GSMclowns]

When I first started my reef tank, I was quiet concern with getting an accurate Alk reading for my tank as well. I too bought multiple test kits from different brands and tried them all. Most of the time, you will never get a same reading with multiple brands. What you want is a test kit that would give you a consistent reading. I always use Salifer for Alk. Is it the most accurate kits on the market? I have no idea but I do know one thing is that it will give me a very consistent reading. If I were to test my tank now, I would get about 9 and if I were to test it after 10 minutes or so, I would get close to 9, plus or minus a bit. I tested multiple test kits and most of them differ other about 2 points in Alk. so that why I always aim for 9 for Alk because if my kit was wrong, then my true Alk would be around 7 or 11 and it is still within the acceptable range.

[Mishri]

yep, what Ron and GSMclowns said, don't chase specific numbers, just look for consistency. reef tanks do well in quite a range of parameters... your corals will tell you more about the water conditions than your test kits will... test kits are more of a tool for finding a problem... and keeping parameters stable.

[AlSimmons]

I'm not sure if somebody already mentioned this or not, but you might want to average out the four test results out and then stick to the one that was the closest.

[tjnorthdakota]

On the red sea kit the stopping point is actually the clearish color right before the orange.

[wrott]

Consistency is the key. If you get the same #s from all kits every week--you're doin good.
I use salifert and if i'm w/in +/- 0.4 MEq/L between testing every week or 2(Ca reactor) it's good. Pick one and go w/ it. No hobby test kit is accurate(quantitative), it's all about quality of measurement(qualitative).

[anthonys51]

All your measurements are basically wrong. It's not you. Our test kits are simple and not commercial grade. They get you in the ballpark. Once you are in the ballpark work on precision, not accuracy. Funny thing about saltwater tanks, precision i.e. stability is more important than any one number. I mean just go read a thread on what the "optimal" parameters are for your type of tank. There is always a range. Ask anyone what is more important a specific number or a stable tank. Choose a kit. Test a LOT. Test the same way, in the same lighting at the same time of day. Anticipate what the number is. If its not what you expect, test again. If it still not what you expect, check your corals/livestock.



IMO it is best to be precise with your measurements and learn the way your fish and coral behave because the dirty little truth is your numbers are wrong. But at least you're in the ballpark...



Great answer. Use the test kit that is easy for you If you test and get 4 different results form the same test kit. Then that's bad but To get 4 different results from 4 different one is ok. Witch one is right. No one really knows only way to tell is to test a know solution with all 4 and see witch one is closest


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[disc1]

And do you really care if it is exact? Let's think about that. Which test kit would you rather have.

The Accurate Kit:
Always gives a value within 0.5dKH of the real value, but could be off in either direction. So if it says 9.0 you know it is between 8.5 and 9.5 for certain.


The Precise Kit:
Never gives the right value. Is ALWAYS low by EXACTLY 3 dKH. So if it reads 9 you know you have 6 on the nose.

[reefdiculous]

Hey guys,

I was away on business for the last few days and just read all of your posts! I happened to pick up new reagent for the Red Sea Pro Alk test at the LFS on the way home tonight. I tested my tank at 8.4 with the new reagent and 7.4 with the old. The Hanna checker and the salifert both came back with around 8.4 as well. So I think that solves the mystery about the Red Sea Alk test.

I think the reagent was maybe bad (not old, both the new and old reagent have nearly the same exp date). The old reagent had a pale orange end color and the new reagent had a deeper red end color (see attached pic).

Anyways, I realize now that I shouldn't get too caught up on the test accuracy. The big take away from this thread is to look for consistency and strive for stability and that it's not about finding the exact correct value :)


Thanks again guys!


And do you really care if it is exact? Let's think about that. Which test kit would you rather have.

The Accurate Kit:
Always gives a value within 0.5dKH of the real value, but could be off in either direction. So if it says 9.0 you know it is between 8.5 and 9.5 for certain.


The Precise Kit:
Never gives the right value. Is ALWAYS low by EXACTLY 3 dKH. So if it reads 9 you know you have 6 on the nose.