Nitrate Testing Accuracy (false high readings) & Water Change Implications

[NW Cichlid Keith]

I saw a video on YouTube (can't find the link now for the life of me), claiming that most aquarium test kits are inaccurate and almost always Overstate what the actual nitrates are. He claimed that LaMotte and Hach were much more accurate b/c they test people water (vs. pet water), which causes them to have more rigorous accuracy requirements. He then compared it w/ state of the art lab equipment and proved his theory. So I just purchased LaMotte test strips, and here is what I found. I tested w/ API liquid, Tetra test strips an d LaMotte test strips on 3 of my tanks. I did a water change, then fed them pretty heavily for a week before testing. Below are the tanks, filtration, and what test results were:

1) 300 w/ large Central Americans mostly - heavily stocked. Filtered by Eheim 2262 w/ Pond Matrix, two huge strawberry pots w/ Hydro Sponge filters and bags of pond matrix (for nitrate reduction), and a huge pythos. API tested 60, Tetra 20, and LaMotte 8
2) 135 w/ matten filter - many slow growing anubias and java fern - many small/medium fish, but not large a bio load. API tested 15, Tetra around 15, and LaMotte 4
3) 75 heavily stocked w/ 50 2-4" barred midas growouts, Filtered by Hydro sponge filters and huge peace lily. API tested 60, Tetra 40, LaMotte 10

Whoever you talk to for the fish I have, I usually get the recommendation to keep under 40 or ideally under 20 nitrates. So, if you assume that I'm meeting that recommendation, but am over it using the API, do I have a problem? I guess what I'm getting it, is are the recommendations based upon people's experiences under accurate testing, or under the overstated testing? Is it possible that our fish are more sensitive to nitrates than we thought, but our nitrates have not been as high as thought?

 

[Drstrangelove]

http://www.advancedaquarist.com/2012/6/chemistry

Certainly OTC kits used by relatively inexperienced users are unlikely to produce results of the same quality as professional equipment employed by professional testers.

However, in the above link, the author tested OTC kits with relatively inexperienced users and got results which while certainly not professional grade, were reasonably useful for most general hobbyists. (People with expensive setups that are attempting to raise or breed difficult fish may unsurprisingly exclude themselves from the general hobbyist category.)

 

[thebiggerthebetter]

My take is based on the advises of Darrel aka dw1305 on Planet Catfish, who is a high level expert on measuring nitrate. He is a seasoned scientist in the field of waste water treatment and runs a lab on research and quality control... while at the same time he is much into fish-keeping and planted tanks.

I will provide two links for you and anyone else to read where his input clarifies nitrate measurement by home kits.

https://www.planetcatfish.com/forum/viewtopic.php?f=4&t=37146&hilit=nitrate

https://www.planetcatfish.com/forum/viewtopic.php?f=4&t=36231&hilit=nitrate

But the gist of it all to me is that:

-- there is no way for us to measure nitrate accurately at all (because there is way too much interference from other similar anions in any typical fish tank water; in other words, the reading cannot be done specifically and be attributed solely to nitrate, as it can be in the cases of ammonia/ammonium and nitrite, but it has contributions from other anions, which can be present, just like the nitrate, at various concentrations; this may explain in part the differences you see in your different brand tests - the tests may have a varying sensitivity to the interfering anions, in addition to varying sensitivity or accuracy for nitrate)

-- I believe that, absent significant water composition changes (which can be brought about by switching a water source or a substrate or a change in diet or an addition of a medication, etc.), the relative reading of the nitrate test results can be relied on to make sensible decisions on one's water change practices.

For instance, if your nitrate reading has gone from 20 ppm to 40 ppm, again absent any significant changes mentioned above, then likely your nitrates have doubled. But in reality the nitrates could have been at 5 ppm and went up to 10 ppm, or they could have been at 80 ppm and went up to 160 ppm.

My limited understanding is that acute toxicity of nitrate begins in the several hundred or 500+ ppm. Long-term exposure to low levels of under 100 ppm varies from fish to fish, with some seemingly oblivious over their normal life span while with others getting affected, even getting sickly and wasting away.

It's worth noting that nitrate reading is zero ppm in all major rivers in the world.

HTH.

 

[squint]

The cadmium reduction method and its variants are very technique sensitive. The other issue is that cadmium is an environmental hazard so there is a fair amount of research into alternative methods such as using enzymes to reduce nitrate to nitrite. Most (all?) nitrate tests involve reducing nitrate to nitrite in some fashion and then performing what is essential a nitrite test. Obviously, any existing nitrite will added to the total. However, nitrite levels in aquaria are usually far lower and thus don't skew the results much. I don't think the same can be said for wastewater.

When I looked for the most affordable accurate nitrate test years ago, I came up with the Hach DR/890 (now supplanted by the newer DR/900) and the chromotropic acid method of nitrate testing.

I recently purchased some 100 mg/L NO3-N (443 mg/L NO3-) standard solution and will be diluting it to 5, 10, 20, 40, 80, 160 and testing the API nitrate test in the near future.

 

[RD.]

I haven't tested nitrates in one of my display tanks for as long as I can remember, I suspect well over a decade. With large frequent water changes, and bio loads on the relatively low side, I use the overall growth and health of my fish as my guide, and as stated above, with zero being the constant in nature that seems like the best goal one can have.

 

[squint]

Chloramine can pass through the gills while nitrate cannot. Chloramine, like nitrate, causes methemoglobinemia. One study found that fish exposed to 1.5 ppm chloramine for 40 min had 32% methemoglobin. A study on nitrate toxicity found that exposure to between 2,200 and 4,400 mg/L NO3- resulted in equivalent methemoglobin content (22.5-44%).

Now consider that most people add dechlorinator to the tank and then start refilling it. A masters thesis on kinetics of tap water dechlorination found that it takes several minutes for a dechlorinator to react with chlorine. The patent for ClorAm-X further states:

With this invention, neutralization times vary from one to five minutes for “free” chlorine (hypochlorites), ten to thirty minutes for chloramines (“combined" chlorine), and twelve minutes to one hour for free ammonia.

So, it's possible a typical water change causes as much methemoglobinemia as chronic exposure to 4,400 mg/L nitrate.

 

[Coryloach]

For the same reasons I don't test for nitrates either. I use a conductivity(TDS) meter. If the tank's water measure has deviated from the tap's reading, then water has become more conductive, i.e. there's waste build up and water changes are needed to bring the reading back to tap water. I consistently keep tanks to tap reading in line, even after years of running the same tank....and for me this method has been the most efficient and reliable in terms of water quality, my happy and healthy fish being the proof for it.

But as R.D. says, in a reasonably stocked tank one large water change a week(50 to 80%) is enough to bring tank and tap water level with some exceptions from time to time. In a heavily stocked tank you need way more than that.....As a reference, I've got roughly 13 clown loaches, 9 adult denisons, 5 SAEs and a bunch rasboras, a few kuhli loaches, a few corydoras in a 240 G tank. I have humongous emerged plants that by the way are chronically nitrogen deficient. I do one large weekly water change. Other people, in the same tank volume would have way more stock......i.e. needing way more effort to keep tap and tank's TDS in line....

As for nitrates, it's worth mentioning that my tanks have never had much of a nitrate reading due to high plant mass. TDS(conductivity) however, increases if water changes are not done. People that have never used a TDS meter and rely on nitrate testing and artificial nitrate removal may be oblivious to their water quality.....because nitrate is not the only issue at play...

 

[squint]

Nitrate is so non-toxic to fish older than fry that it only serves as a rough indicator of when to change water. A glance at the calendar can easily substitute. I weigh out each feeding so I'm feeding the same amount everyday but I also keep a running total of how many grams of food has gone into the tank since the last WC. I haven't compared this against nitrate levels but I bet it's fairly predictive since I only feed one type of food.

 

[duanes]

When I worked in a lab, I would bring in samples from my tanks, and run them on a photo spectrometer that cost more than my truck.
The reagents used were always freshly made, and the spectrometer calibrated weekly.
I also had to compare results with nitrate test strips we used in the field, and the pro quality strips from Fisher Scientific were usually very close.
The thing that could skew test results most often, were "old" reagents and most importantly, tainted glassware. Rinsing 3 times with DI water between each sample was standard practice to remove and residual, and thoroughly cleaning glassware just as important. When dealing with tiny aliquots of liquid, and PPM, even the slightest left over residual in a tube can create very skewed result.
And although nitrate may not be acutely toxic to fish, it can create chronic problem, and be a stressor the leads to HLLE and other health problems as fish age.
Most nitrate research is done on aquaculture species, which are not meant to live long, but just to quickly put on size, and be presentable enough to be sold for human consumption.

 

[thebiggerthebetter]

When I worked in a lab, I would bring in samples from my tanks, and run them on a photo spectrometer that cost more than my truck.
The reagents used were always freshly made, and the spectrometer calibrated weekly.
I also had to compare results with nitrate test strips we used in the field, and the pro quality strips from Fisher Scientific were usually very close.
The thing that could skew test results most often, were "old" reagents and most importantly, tainted glassware. Rinsing 3 times with DI water between each sample was standard practice to remove and residual, and thoroughly cleaning glassware just as important. When dealing with tiny aliquots of liquid, and PPM, even the slightest left over residual in a tube can create very skewed result.
And although nitrate may not be acutely toxic to fish, it can create chronic problem, and be a stressor the leads to HLLE and other health problems as fish age.
Most nitrate research is done on aquaculture species, which are not meant to live long, but just to quickly put on size, and be presentable enough to be sold for human consumption.

Glad to see a fellow chemist in the room.