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Nitrate test kits.

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Can anyone recommend a decent nitrate test kit?

I have been using API, I'm on to my third nitrate kit and they all seem to stop working after a short period of time (maybe 3-6months?). I go from a steady 10-20ppm to 40-80 and no matter how many water changes I do, the result stays the same.

Thanks in advance!

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I've never had this issue with api test kits but I've heard of people that have.

A person on a marine page got their water lab tested and the api kit was more accurate than saltifert and Hanna checker, i was considering Hanna before I read about that.

Whatever you chose always use liquid tests, the test strips that you dip in the water are so inaccurate it's hilarious.

I had one of the strips tell me that my fully planted tank had a nitrate reading of 160.

Cheers mick

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I have seen many people battling “high nitrates” in tanks in recent times on the Facebook forums. They do water change after water change but their nitrate readings remain high. The common factor – API test kits. So I did some tests for myself. I tested a water sample with two API nitrate kits, and one JBL kit. All kits were within use by dates and had been stored properly since purchase.

Older API kit - 40 ppm (3 months before expiry, bottles well used but shaken well before every use)

Newer API kit - 160 ppm (2+ years to expiry, bottles used for one or two tests only)

JBL kit - between 5 & 10 ppm

The tank is a large moderately stocked tank running a large Marine Pure block in the sump for nitrate reduction. I would expect nitrate levels to be low.

I have since made a comparison using JBL and ELOS kits on another sample and they gave identical results.

While the API nitrate kits appear to be particularly problematic, I no longer trust the API nitrite kits either. I had a situation with dead fry in a tank. API kits indicated water was fine, while JBL showed elevated nitrite. Without the JBL kit I wouldn’t have known how to deal with the problem.

I am a degree qualified engineer with 25+ years’ experience in Test and Evaluation. I suggest if I can’t get repeatable results from a test kit then they aren’t suitable for the general hobbyist.

I used to recommend API kits to others as a relatively affordable, readily available option. I no longer do. False negative test results mean problems can’t be identified. Excessive readings lead people to take drastic, unwarranted interventions on their tanks.

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Thanks everyone for the advice, I'll be visiting the tech den this weekend for a new kit.

I've been doing quite large water changes on a 1800L pond and with the new water being so cold, the heaters have to play catch up. So it seems I've been wasting water and electric thanks to API. :frusty:

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I left a review of the salifert kit last month on the tech den website.

Product Review June 2, 2015

Reviewer: Daniel from Deception Bay, QLD Australia

Great product, the 25 and 50ppm markers help fill IMO the gap in a problem with the API test kit, I have always had trouble telling the difference between the colour difference of 20 & 40ppm, also it allows you to get greater accuracy under 10ppm.

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Havent had a problem with api nitrate kits when they are used correctly (shaken) and I dont want to brag but I have done a lot of tests. Have had customers with kits reading out tho.

Big thing to watch is evaporation. Put those lids on straight after doing test AND make sure correct lid or tests are contaminated.

Some chemicals will trip out test kits, but most often its a case of OTS. Clean filters and vac gravel.... then try water change. Tends to prevent nitrate bounce back.

Otherwise salifert is good.....

Only API kit I have an issue with is phospate as it only reads as low as 0.25ppm and I usually need lower to be proactive in controlling it.

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I used to be of the same opinion. For a long time I've been telling people the problems were caused by not shaking the reagent #2 bottle sufficiently. It wasn't until I got the results above from kits that I knew the history of that I realised the problem is more significant. When I used either of those two API kits on tap water or distilled water I got a zero result, but with water with any trace of nitrate I got a very high reading. Both of those kits have had the sh*t shaken out of them each and every time they were used, and both have been stored in appropriate conditions since purchased. The kit which gave the worst reading was near new. We aren't talking about a batch problem here.

I suspect the issue is because the reagent #2 precipitates out of solution easily, and hence concentration varies wildly. I'm guessing brands which provide the reagent as a powder (such as JBL, ELOS and several others) likely provide more accurate, repeatable results.

One of the problems is that we accept that the result we get from our kits are correct.Unless we suspect there is an issue and make theeffort to compare results with another brand, how would we know any different?

Edited by humbug
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It's food for thought. Certainly interesting results. Much appreciate the information.

What would be ideal would be testing against a standard, then we'd know for sure what's going on and how accurate they are. Some comparison testing :). I guess this is partly why EI dosing for planted tanks came about?

My main experience is with the API liquid test for nitrates. Generally in tap and tank I've found it consistent. Could well be wrong answers but generally makes sense with tank changes. I find the colours really hard to read though.

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Powder reagents are harder to measure...... prefer to avoid where possible personally. Not that its ever possible in marine tho :(

Perhaps a better way to test results is to make up a known nitrate solution and then compare test results against it.

As to reading results, if its above 40ppm I tend to dilute sample with RO water, then multiply result.

Eg put 2.5ml of aquarium water into test tube. Then add 2.5ml of ro water in. Add nitrate test reagents. Double results.

This can help give more accurate readings.

Other variables include

☆discoloured test water eg from tannins or food.

☆waiting different times after test to read results.

Understand I am not doubting people having problems with a product. More just sayin' this is the most used nitrate test kit on the planet. It aint perfect but its pretty dam good all things considered.

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I have found in my marine tank I get different test results at different times of the day, not sure if fresh is the same as i don't test fresh unless something stops breeding. I record test results when fish breed and if they stop I test and correct the conditions they need.

With marine I find a test result at 8:30am and 1:00pm are totally different so every test is done at the same time of day now to give more accurate readings, not just nitrate but all tests.

Has anyone noticed the same thing in fresh tanks, I'm always in the fishroom at the same time of day so haven't tested if time has an effect.

Cheers mick

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The big thing I don't understand is why I have 3 kits that give different readings, now I just look at it and see if it is constant I use the kit that says 40 and as long as it stays at 40 I take that as a minimum reading.

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I’ve actually seen a few shops defending the API kits, which got me thinking. These experiences seem to be counter to the experience that so many hobbyists are having. Here’s one possible explanation . . . but obviously only a theory.

I’m guessing AoA and other larger businesses have a pretty good turnover of product, and hence the API test kits don’t stay on the shelf for too long. Shops offer water testing as a service for customers, and the larger, well patronised shops do a lot of these tests, just as you have suggested, Donny. You take the relatively new bottles from stock, use them for customer testing, and they are consumed pretty quickly. They never really have time for the bottle to sit and the reagent to precipitate out of solution.

Now look at a general hobbyist. While setting up a new tank, there might be quite a bit of testing until things settle down. But once a tank is established, how often do we really test our freshwater parameters? The conscientious person may test once a fortnight, or once a month. More experienced aquarists generally only test when there is a sign of an issue.

An API nitrate test kit is apparently good for 90 tests. Even at one test per fortnight, with a couple of tanks that kit will last the best part of two years, and that can still be well within the expiry dates of these products.

I suspect the difference in perception of the accuracy is because the kits being used by the larger shops are being shaken on a very regular basis (perhaps several times per day?), while the home kits are sitting on a shelf for a fortnight, or a month, or even longer, at a time. Even the newly opened kit that I tested gave crazy results. I’m guessing these products have a three year shelf life, and this bottle have already been sitting somewhere for the best part of a year before it came into my hands. I can assure you I am well aware of the need for shaking these products, but no amount of shaking of that particular bottle could achieve anything like a sensible test result!!!!!

Irrespective of the cause, surely we should be able to expect that these products would remain reliable for more than a couple of months?????

This isn’t an isolated instance. I’ve seen exactly the same problem being faced repeatedly by hobbyists on the Facebook groups, which is what originally got me digging further to find answers. These are not issues of lack of tank maintenance, insufficient substrate vacuuming etc, etc. This is clearly a product giving false test results. lgw has obviously experienced the same thing, which is what started this particular thread. Cam07 has had similar experiences. Surely ANY test kit sold to the hobby should give repeatable results with a measure of accuracy when used by a hobbyist in accordance with manufacturer’s instructions? As consumers, we have a legal right to expect that products we purchase are in fact “fit for purpose”.

I agree that using a powder is marginally more difficult, but if it’s the difference between getting a correct result and a downright misleading result, the decision is an easy one for me to make.

I’d dearly love to be able to undertake some controlled testing of different products to get some unbiased comparisons to help answer some of these questions for hobbyists. There is so little information available, and there is certainly a need. Problem is it takes money . . . . . . .

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We sell thousands of these kits at AOA and its literally 1 in a 1000 people that have drama with a nitrate test.

As to making up a nitrate solution to test, a few bucks would do it and even then because you'd buy a bag rather than a gram.

Over all I consider the API master test kit to be one of the best tools new aquarists have available to really do well in this hobby.

I suspect that lends a bias tone to my posts. I am hoping it is not coming accross as just me refusing to recognize your issue with your kit. More just that this is a rare occurrence and likely not indicative of a product wide issue. We encourage feedback on stuff we sell at AOA and people dont hold back lol. This is the first issue I have heard about with this kit in ages.

Last one had so much dried crystals in the bottle thread that I was confident it was caused by evap.

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I do have a link somewhere on comparison testing at a get together but it is dated. Will see if I can find.

This is a great thread - I've resolved to be more skeptical but not throw the baby out with the bathwater. Will pick up another brand of nitrate test kit some stage to test/verify my results. Great posts.

I'll have to check the expiry date on my master kit. I generally test now every fortnight for phosphate and nitrates as a minimum. I do regularly testing as have never taken to the EI dose, water change to reset schedule. I'm not that good at tank stability.

Elsewhere I've seen issues with API master kit but they are rare.

API gh test I've had over the top results from but was out of date (gift from lfs).

API cardboard test strips I have but don't use. Don't trust.

API ph test ok vs digital ph meter.

API ammonia I think ok. Tap water is 0 and I have gotten an ammonia reading from a dissolved API root tab in 20 litres of water. The reading could be inaccurate (now I'm wondering on previous high ammonia readings where fish were fine) but I just need to know if ammonia is present so happy there.

My only other thought is to wonder if test methods using a different process will give the same result (even though they should).

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Heres a copy paste from theplantedtank forum.... bit intense buuuut figure might be of interest to some.

Calibrating Test Kits Calibrating a test kit means using that kit to measure some water samples with known concentrations of the substance being tested for, and using those test results to verify that the test kit is accurate, or to train yourself to recognize the colors that correspond to the concentrations you want to test for. Hobby test kits are not laboratory quality tests. That means we don’t need extreme accuracy in the standard test solutions we use for calibration. If we have a good quality gram scale, with +/-.01 gram accuracy, and good laboratory glass graduated cylinders to measure water volume, there are other articles that tell how to make very accurate standard solutions. The methods described here are for use with ordinary kitchen measuring equipment, measuring spoons and cups. And, the Fertilator calculator on APC was used to easily calculate how to mix these. Nitrate Test Kits First, buy a gallon of distilled water from your local grocery store. Use that to make the test standard solutions. 1. Add 1/4 teaspoon - a level measure, not a heaping measure - of KNO3 to 4 cups of distilled water (one quart). This gives you 4 cups of 800 ppm nitrate water. 2. Mix 1/4 cup of that 800 ppm water with 1 3/4 cups of distilled water. This gives you 2 cups of 100 ppm nitrate standard water. 3. Mix one cup of that 100 ppm water with one cup of distilled water. This gives you 2 cups of 50 ppm nitrate standard water. 4. Mix one cup of that 50 ppm water with one cup of distilled water. This gives you 2 cups of 25 ppm nitrate standard water. 5. Mix 1/2 cup of that 25 ppm water with 3/4 cup of distilled water. This gives you 1 1/4 cups of 10 ppm nitrate standard water. 6. Mix 1/4 cup of 25 ppm water with 1 cup of distilled water. This gives you 1 1/4 cups of 5 ppm nitrate standard water. 7. Use your test kit to measure the nitrate concentration in each of the 5,10,25, and 50 ppm nitrate standards. If you wish, add the 100 ppm standard to that set. 8. Compare the colors of those to the color card for your kit, and either verify the accuracy of the kit, or use those colors to train yourself to recognize the colors. Your nitrate test kit is now calibrated. You can store the standard solutions in tightly sealed bottles for an indefinite period of time for future calibrations. Ideally, you calibrate the kit each time you use it.
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Awesome input guys, thanks for that.

Here's how I've always used the API nitrate kit.

Step 1. Scoop exactly 5ml (according to the test tube) from tank or pond.

Step 2. Shake bottle 1 (not in the instructions, I do it anyway lol) and add 10 drops to tube.

Step 3. Give the test tube a quick shake.

Step 4. Vigorously shake bottle 2 for 30 seconds and add 10 drops to tube.

Step 5. Shake test tube for 60 seconds.

Step 6. Let the tube sit for 5 minutes.

Step 7. Hold tube against white part of colour card in a fairly well lit area and try to match the colour to the card (easier said than done).

Here's a graph showing my nitrate readings, water change percentages and filter maintenance. Sorry if it's not very clear, it works for me haha.

You will have to ignore the nitrate readings on the 20/04 and the 04/05, I marked them on the wrong dates :frusty:

Red is water change %. Blue is nitrate ppm. And the green line is when I service the filter.


You will notice I've marked the nitrate readings as 15ppm and such... I do this when I can't decide if the colour is 10 or 20 etc.

Edited by lgw
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