# Test kits: the good, bad and ugly



## Newt (Apr 1, 2004)

Looking for feed back on test kits for the hobby. Namely NO3, NO2, NH3 and PO4 but also interested in K2SO4, Fe, etc. I test my water after a water change and adjust as necessary.

My experiences:

Nitrate: I've mostly used Aquarium Pharm. Its not expensive but accuracy seems limited to 0 to 20ppm. After that you really can't tell. Even above 10ppm can be a guess.

Nitrite: Aquarium Pharm: inexpensive, easy to read. 

NH3: Aquarium Pharm: inexpensive, easy to read. 

PO4: I've mostly used Seachem. A bit pricey but I like the reference solution as a check. I tried the Aquarium Pharm one and found it NOT easy to read.

K2SO4: LaMotte. Expensive. Seemed to work well but as with any kit who knows.

What do you all use and what's your experiences/thoughts?


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## rjordan393 (Nov 23, 2012)

As many will say, you get what you pay for. Test strips are frown upon because all you get is a range.
A good test kit will give you numbers. But then, some of them are open to the users perception.

I read an article years ago, that stated that test kits are most accurate at the middle range.
When I got into the fresh water hobby, I started out with the "Nutrafin" test kits and was satisfied. But I started to have doubts and purchased a more expensive kits from the "Hach" company. When I tested Nutrafin NO3 and their PO4 kits against the more expensive Hach kits, they both gave nearly the same results. This speaks well for the Nutrafin product line of tests.
Now the Nutrafin line of kits cost anywhere from $12.00 to a bit higher I believe. I believe you will do well with the Nutrafin test kits.
Now I only know of one manufacturer that offers a kit for testing fresh water potassium and it is pricey.
The LaMotte company has this kit and it is around $60.00 plus shipping I believe.
But all is not lost on that parameter. The online companies that sell chemicals to hobbiest's such as nitrate, phosphate etc also includes potassium in their mixes. So it depends whether you need a test kit for potassium.


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## Newt (Apr 1, 2004)

Great info. I'll look into that brand.

You reminded me that I have a Hach PO4 test kit 0 to 50ppm and it uses has a reference wheel. The reagent packs are old.

Interpretation of color rendering kits is a must and IS open to interpretation.

I will say that API's Quality Control is horrible from kit to kit.


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## rjordan393 (Nov 23, 2012)

I test my parameters after a water change. I have the Hach nitrate nitrogen, ortho-phosphate and iron test kits and the LaMotte potassium kit. I like the Hach kits that uses a color wheel. It is more precise. The initial cost is high and the replacement reagents are just a few dollars more then replacing the whole Nutrafin kit. I think most fish stores do not sell replacement reagents for any of water testing products. So one has to buy the whole kit.
Now I have a few things to say about potassium. My past test results were indicating too much in my water and I was over dosing. So now, when I dose, I keep the expected results lower then my expected results of nitrate. I do not know if this is true or not, but I read an article that stated that it is suspected that too much potassium can interfere with the uptake of nutrients.


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## Newt (Apr 1, 2004)

rjordan393 said:


> .............................................................. too much potassium can interfere with the uptake of nutrients.


 I believe that is correct.


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## ray-the-pilot (May 14, 2008)

Believe it or not it doesn’t matter much which kit you use if you follow some basic chemistry.
Firstly, you have to realize that the color reference you have with your kit may be unreliable because color development depends on a lot of factors besides the concentration of the substrate. Things totally out of your control like temperature, age of the reagents, printing errors in the package and a gazillion other things make using the reference colors in any kit questionable. 

So how do you get around this problem? You always need to run a minimum of three tests at the same time. 

The first is a blank. This uses purified (ie distilled) water in place of the sample. 
The second is a control. This uses a sample with a known concentration of substrate at the concentration you expect in place of the sample.
The third is, of course, your sample. 

You have to run all three tests at the SAME TIME and under the same conditions. When the colors develop you can expect that the blank should have no color and the control will be the same color as the equivalent reference on your color chart. If this is not true than you cannot use the color chart for your estimate directly. 

What you have to do is correct the color chart to your control. If the known concentration of the control is 20 ppm and the reading on the reference chart is 30 ppm then your chart is off by 20/30. Then when you check your sample and it reads 40 ppm you have to multiply this result to get the corrected answer: 

20/30 * 40ppm = 27 ppm. 

If you are consistent when running all three tests, you can use some really bad reagents and still get good results.


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## Newt (Apr 1, 2004)

Very interesting Ray and most likely correct.

I have tried doing something similar using the Fertilator and my digital scale. I mix a known amount of KNO3 into a gallon of distilled water and do a test. I use that to compare.


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## ray-the-pilot (May 14, 2008)

Newt said:


> Very interesting Ray and most likely correct.
> 
> I have tried doing something similar using the Fertilator and my digital scale. I mix a known amount of KNO3 into a gallon of distilled water and do a test. I use that to compare.


That is exactly right. You can do the same for phosphate as well.

I forgot to say that I use LaMotte kit reagents for K, P and N. 
I have not found any test sensitive enough to test for Fe. 
I use the APHA standard method for calcium and magnesium, which is similar to the LaMotte kit. I've tried the LaMotte kit and it works OK but the titration is not very precise (at least from my perspective). I think for getting an idea of where your water is relative to those substrates it works well.


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## Newt (Apr 1, 2004)

LaMotte makes great test kits. Pricey but way more accurate than most. I also find them hard to find.
I have a potassium kit by LaMotte. I like the Seachem kit as it has a reference solution.

I find it difficult to make reference solutions for PO4 as the amounts for 1 gallon are small. My digital scale does 0.00 but I don't trust anything in the hundredths.


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## Seattle_Aquarist (Mar 7, 2008)

Hi Newt,

I check my water parameters about once a month unless it is a new tank or I am having issues. After trying several kits I now use:

PH = API
dKH = API
dGH = Sera (used to use API but with our low hardness here it was hard to accurately determine the color change)


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## Newt (Apr 1, 2004)

I now check after each water change and adjust as necessary for fertilization.
I really need a good NO3
Seachem PO4 kit is decent. I did not like APIs kit.
pH, GH and KH by API are close enough for those parameters.


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## ray-the-pilot (May 14, 2008)

Newt said:


> I find it difficult to make reference solutions for PO4 as the amounts for 1 gallon are small. My digital scale does 0.00 but I don't trust anything in the hundredths.


A digital scale gives you a lot of power! You can make serial dilutions of concentrated solutions to even microscopic amounts of substrate. Here is how to do it:
Since the Fertilator only knows liters and gallons you have to remember that 1 gram of water = 0.001L. 
The next piece is the capacity of YOUR scale. Say it is 500g. That will be the biggest size solution you can make.
Now go to the Fertilater and put in aquarium volume 0.5L (500g x .001L/g = 0.5L). Then play with the amount of substrate you add until you get the right ppm of PO4. For example when I use KH2PO4 as my substrate I found that if you add 0.00072 g of KH2PO4 to 500g (0.5L) you will have a 1 ppm solution of phosphate. You cannot weigh 0.00072 grams on your scale but if you multiply this result by 1000: 1000 * 0.00072g = 0.72 g you can weigh this amount. 
So place a plastic cup that can hold 1/2L on your scale and tare it off. Then add 0.72g of KH2PO4 into the cup. Then add sufficient purified water to make a final weight of 500g. 
This solution is 1000x stronger than you want. It will be a 1000ppm reference. 
Now take another plastic cup that holds 1/2L and tare it on you scale. Weigh in exactly 0.50g of the 1000ppm reference and then add sufficient purified water to make 500g. 
This solution will be 0.5/500 = 1/1000 the strength of the 1000ppm reference solution or
1000ppm *1/1000 = 1ppm
That was a lot harder to write out than it is to do. Here is the short answer.
Make a solution that is 10x, 100x or 1000x the concentration you need. Then use your scale to make the appropriate 1/10, 1/100 or 1/1000 dilution.


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## Newt (Apr 1, 2004)

Thanks Ray


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## AEWHistory (Jul 6, 2008)

I hope this doesn' I jack the thread but I think this is a relevant question: how much does expiry matter? For example, I had left the hobby for three years or so recently and just starting back up. At this point all my test kits are past expiry from a few months to a few years. Are they of any use? I tried a strip recently on my house tap water and got the results I had expected, but this was a very rudimentary test at best and wanted to ask people who know better. Thanks!


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## Newt (Apr 1, 2004)

I have seen some kits with expiration dates. i.e. LaMotte but not kits like API and Seachem. I would say if they give an expiration date then the reagents they use must go bad. This may also be true for the other kits that don't have an exp. date. I would think it would be beneficial to the manufacturer to give a exp date. That way you'd buy a replacement.

Welcome back to the hobby.


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## ray-the-pilot (May 14, 2008)

AEWHistory said:


> I hope this doesn' I jack the thread but I think this is a relevant question: how much does expiry matter? For example, I had left the hobby for three years or so recently and just starting back up. At this point all my test kits are past expiry from a few months to a few years. Are they of any use? I tried a strip recently on my house tap water and got the results I had expected, but this was a very rudimentary test at best and wanted to ask people who know better. Thanks!


You never know if a new kit is ok unless you run a positive and negative control. If you do that and you get the expected results you can be pretty sure your test is accurate. So run three tests, one using purified water, one using a positive control made up to a known concentration and the third being your sample. 
If the purified water gives no color, and the control gives the correct color, your sample should test OK.


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