View Full Version : Which test kit should I trust for nitrates?

05/09/2011, 07:49 PM
Trying to get an accurate reading on my nitrates and I have 2 kits giving me 2 totally different readings.

first one is an API kit I bought a month ago, reads in the 60+ range (red)

next one is a salifert that is expired by 6 months reading 0.2 nitrates on the low range.

I assume the best answer is to get a new salifert test kit and call it a day, but for right now which one should I trust?


05/09/2011, 07:53 PM
This is what I want to avoid- also curious which would be more accurate.

05/09/2011, 08:06 PM
i can't help but think there is some user error, or something going wrong. Even expired by a month and totally different tests should not be that out of whack. Are you sure they are both nitrate. one could be nitrite. Start from the beginning and look for the obvious.

05/09/2011, 08:09 PM
ALL my LFS use API, they swear by it. One is quite succesful, with great customer feed-back. I have seen them keep the most delicate of creatures for lengthy periods of time on these kits.

05/09/2011, 08:53 PM
Do they read the same units?

05/10/2011, 06:01 AM
yes, there both nitrate test kits, yes they both read the same units. all good guesses to what the problem might be, cant wait to hear from someone that really knows their stuff.


Randy Holmes-Farley
05/10/2011, 06:15 AM
Nitrate kits are notoriously inaccurate. Many people who test multiple brands get wildly different answer on the same aquarium. I don't have a specific brand I recommend.

john f
05/10/2011, 06:26 AM
Randy is correct, but I have always felt I had fairly consistent results from Lamotte's test kit with comparator.
The reagents must be new IMO, and even with my Lamotte tests you can notice a lot less sensitivity as the reagents age.
Some fish stores may have test kits on the shelf that are quite old, and have also been in the distributors hot warehouse for many months.

05/10/2011, 07:30 AM
Trying to get an accurate reading on my nitrates and I have 2 kits giving me 2 totally different readings.

first one is an API kit I bought a month ago, reads in the 60+ range (red)

next one is a salifert that is expired by 6 months reading 0.2 nitrates on the low range.

I assume the best answer is to get a new salifert test kit and call it a day, but for right now which one should I trust?


I use both the API and Salifert kits and get good agreement.
Your Salifert if expired will NOT provide you an accurate measurement.

The API is ok to get a ballpark value in the low range, but the Salifert on the low range is better to get a more exacting value.

05/10/2011, 07:47 AM
I like the LaMotte kit also. You just have to do a little conversion. It measures nitrate-nitrogen, NO3-N x 4.4 = NO3-ppm.

05/10/2011, 07:48 AM
i use api

05/10/2011, 08:34 AM
Just because they both read nitrate doesn't mean that they both read the same units. Some report ppm, and others convert to nitrogen. I have never used the API test. You should also make sure that they both test the same range. If one test "tops out" at a lower value, and the actual measurement is above that, then that may be the problem.

Please be careful with the can't wait to hear from someone who knows their stuff line. I have a phD in analytical chemistry and spend most of my days testing water for something or another. I am pretty sure that I "know my stuff", I just don't know your low grade kits that well. And I'm pretty sure that RHF falls into the category of folks that know what they are talking about too. But if that help is not appreciated, then good luck.

05/10/2011, 08:51 AM
disc1, I think he was talking about waiting to hear from someone like you or Randy that has much more experience than me, the newbie. I would say your phD makes you more than qualified to discuss chemistry issues. He just wanted to heard from someone that has more posts than he does, even though the number of posts to this forum does not equate to a greater level of experience or knowledge.

05/10/2011, 08:52 AM
I use the api and salifiert. The api works fine for levels over 5ppm but you can't get much specificity between that and 0. The salifert gives better low range info.

05/10/2011, 09:56 AM
Unfortunately, Salifert does not offer an MSDS for their kit that I can find. SO I am not real sure what is in that one. I suspect that the two kits handle the reduction of nitrate into nitrite prior to reaction with sulfanilamide in different ways. Tha API MSDS lists no reducing agents, so let's assume that it is not cadmium. This means that they probably suffer from different interferences. Things like amino acids can throw some nitrate tests off. FWIW, I've read a lot of reports this morning from hobbyists who complain about API giving high results.

05/10/2011, 10:05 AM
BTW, this is why I hat colorimetric tests. Nothing compares to my triple quad MS. Now there's some accurate results.

05/10/2011, 11:07 AM
Didn't mean any disrespect in what I said, and actually praised the attempts at the help. I could care less about post count, all I'm looking for is a little help from reliable sources relating to the topic at hand (and it seems I found one with a freakin PHD in chemistry trying to help out . . . how cool is that?). I know my test kits suck (a decent expired one and a bargain bin API) and thats why I'm asking which one might be "more accurate"

I'll look into the lamotte kits, and might end up getting another salifert one this week if there in stock at my LFS. Is there any other test kits people recommend I should be looking into? I'd like to keep more demanding species of corals and need to start paying more attention to my levels.

Thanks for all the help.


05/10/2011, 12:49 PM
Sorry to jump at you then. My mistake. I've had my hackles up all day.

The short answer is that I wouldn't trust either at this point. 60ppm is pretty high, so if that one is right you should be able to see some symptoms of high nitrate in the tank. 0.2 is really low, but you said that kit was out of date.

The long answer is to grab one of the standard solutions that come with some kits and try the test out on that. That allows you to check the kit as well as your procedure. If they both read right for a standard solution, then it's probably something in the tank water that is interfering with the colorimetric test.

05/10/2011, 01:34 PM
Given the continuing issues with test kits, particularly nitrate kits, I'd probably watch the animals carefully, and not worry excessively about the actual level. Given that the Salifert has expired, I'd be inclined to trust it less, though.

05/10/2011, 02:03 PM
Just did a 40 gallon water change on a 200 gallon setup and a half hour later the API test kit is still showing super high nitrates. /sigh

Disc, I dont think either of the ghetto kits I'm using come with a standard solution,

Bertoni - Thanks, thats what I've been doing all along and the fish all seem fine, I'm looking to start getting into some of the higher end chalices and SPS tho and would really like to get a handle on everything before I go out and spend a crap load of cash only to end up with skeletons. What nitrate kit do you use?


05/10/2011, 02:17 PM
I have used Salifert, IO, and Red Sea. The Red Sea was problematic.

05/10/2011, 02:35 PM
With all do respect any brand test kit can go bad.
Jonathan hit the nail on the head monitor how your fish are acting if the Nitrates are above even 40 ppm you will see heavy breathing and most likely the fish will be at the suface gasping.
Im no expert by any means but this is from what Ive seen over the 30 + years Ive been around the hobby (still a rookie).
Here recently I was at my friends fish store and noticed the fish breathing heavy and comming to the top surface.
I asked if the tanks had been tested recently he replied yes the employees check it a few times a week he pulled the test log out and they hadnt been tested in months for NO3 so I did a NO3 test (ELOS) came out at 25ppm so I doubled the water volume and it was still at 25ppm so if Im not mistaking this means they are at 50ppm +.
Myself I test for NO3 about every 3 to 4 months always around 1ppm to 2ppm accodring to ELOS test kits I do weekly 25% water changes and feed lightly.
If your budglet allows it there is a company called water testing dot com where you pay for lab testing they send you containers you send back water samples to them they email you the results just if you want to see where you are at now.
Good luck hope you get the answers you need if you are that high just do a 30% water change every other day for a week it should bring them down.

05/10/2011, 08:31 PM
Nitrate itself seems to be safe for fish at 100's of ppm. A large number of people running fish-only tanks have reported numbers in that range with very healthy fish. Gasping at the surface likely is due to oxygenation problems.

05/10/2011, 10:22 PM
Nitrate does not harm fish, ime. It may brown some corals ; cause some to recede and fuel nuisance algae. While nitrates are <0.5 in my system and have been so for several years, I've seen the effects of high nitrate3 ( 80ppm) in the past.
Personally, I focus on inorganic phosphate(PO4 species) as well since it can inhibit calcification at low levels and is a serious threat to the types of corals you plan to keep.
I don't have any idea which of your kits is working properly since the variation 60ppm to 0.2ppm is extraordinary. I don't think anyone can answer that question.
Granted accuracy with hobby grade test kits is a problem but most would not see that variation between an api and a salifert absent a kit gone bad or testing error.
For the most part ,the api and the salifert kit will give you reasonably reliable useful information,ime.Cross checking them against each other or another kit is also helpful.

06/16/2011, 09:46 PM
Just wondering if OP ever tried a new test kit. Just curious if nitratea are closer to 0.2 or 60.

Ron Reefman
06/17/2011, 07:29 AM
Are you close to a LFS? Why not take a small sample of your water to them and see what they get. Also take both of your test kits and have them test their water with all 3 kits and see what the results are. I use API & Salifert test kits and I get very similar results from both. And a test kit being just inside or outside it's expiration date isn't an issue. I've had expired test kits (came with other equipment I've bought used) that test just like my new kits, and I've had 'current' kits test way different from mine. Get more data by going to a LFS and doing the tests. Good luck.

06/17/2011, 08:59 AM
IIRC, Salifert Nitrate test can test both high and low range. If it is low range you look through the side, if high range you compare color from the top. I would make sure you are testing correctly. I have used API ever since I started and they have always had pretty decent results.

06/17/2011, 01:33 PM
the salifert kit was bad, nitrates were around 40-60. compared it to another 2 salifert kits, one I picked up and another a local reefers. I know how to read the kit, mine came with instructions too . . . the results coming up with an almost 100% clear solution were hard to mis-read.


06/17/2011, 05:43 PM
and it seems I found one with a freakin PHD in chemistry trying to help out . . . how cool is that?).

Actually 3, Randy Holmes-Farley has a Ph.D in chem from Harvard :D and is director of a research lab. Disc is also a Ph.D as is Nick, aka UVvis. There are quite a few chemists here ;)

Nitrate in the Reef Aquarium by Randy Holmes-Farley.