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

[nzafi]

I am no chemist, and don't have the same level of experience as you guys. All I can say is that I am so much happier after I put in a drip system that changes out about 20% of tank water daily (2gph drip on 180g).

I used to do 50% weekly water changes on my 180g tank and could never get the nitrate to measure less than 40ppm no matter what I did. After introducing the drip system my nitrates always stay less than 20ppm even though I feed a lot more these days. Understanding test kits aren't 100% accurate, I am just that much happier to be able to provide consistent clean water to my fish.

My biggest concern these days is maintaining the filter on my auto drip to make sure no chlorine or chloramine makes it into the tank.

 

[squint]

I forgot to mention that a few years ago I was confused about recommended nitrate levels and took the opportunity to ask the veterinarian the last time I brought my fish in. At the time, I was living near UC Davis, the #1 ranked veterinary school in the country (and probably the world). Also worth noting is that their aquatic veterinarians are the same ones who are caring for fish at public zoos and aquariums. Jobs at public zoos/aquariums are among the most competitive.

Anyway, I mentioned there was a lot of conflicting information (Internet vs. studies) and they said to keep it under 150 mg/L (I'm assuming this was NO3-). I thought that was kind of high but they assured me that it was fine, especially since my loaches are cyprinids.

When I returned home, I began looking at studies more closely and study after study turned up shockingly huge LC50 numbers. Then I began to wonder how the Internet came up with the 20 ppm recommendation. It seemed to mostly be based on personal opinion and the fact that things that are repeated enough times on the Internet become regarded as "fact." It didn't help that nearly all hobbyists don't understand the difference between NO3-N and NO3- and were advocating for 20 mg/L based on some harmful effects at 100 mg/L for fry/eggs in some study. Of course, the study was using NO3-N so the 20 mg/L they advocate is really 89 ppm NO3-.

 

[dan518]

Have you got any links to these studys? Most of the ones i have seen have all been short term, NASA did a long term study which recommended 25ppm as the safe limits.

 

[squint]

The Camargo review paper ("Nitrate toxicity to aquatic animals: a review with new data for freshwater invertebrates") has a good summary of studies. It's from 2005 so it doesn't have the most recent studies. There was one from last year by Monsees with tilapia for 30 days. There was also a study from 1973 that lasted half a year.

Edit: The NASA study was subjecting fry and 1-month old fish to 100 and 125 mg/L NO3-N for 96 hours. That's 443 and 550 mg/L NO3-, respectively. Their recommendation of 25 mg/L NO3-N is 111 mg/L NO3- which is quite a bit to ask of fry.

 

[FreshyFresh]

I definitely respect the science behind this and have some commercial experience measuring water params given we have a boiler system at work.

Thing is, given there's so much that skew the readings, this makes me want to change water in my tanks even more! lol. After all, it's not just because of nitrates we change our aquarium water. IMO, it's important to keep your tank water as close to the parameters of your source water as possible.

For me, I don't care that my API nitrate test kit still reads orange on day 7. I'm still doing a 50% water change at a minimum. There's a week's worth of bodily waste products, food being added to the tank, etc.. in there. Yuck.

 

[squint]

Yeah, I change my water when it's time or because I think it looks dirty. I'm more concerned about pH crashing or ammonia. Those and chlorine/chloramine are far more likely to injure fish (and hardly anybody tests for chlorine).

People with 40 ppm tap water and 80 ppm in the tank shouldn't worry as much as people who started with 0 ppm tap water and also reached 80 ppm.

 

[RD.]

The problem with many aquatic based studies, is as Duane mentioned, they are short term. They are also often designed with a desired result, for commercial purposes. Acute scenarios are great, but for anyone that keeps their fish long term chronic health issues are just as important. I'm a simple guy, following natures lead just seems to make sense. (0 ppm)

BTW squint, you said: "A masters thesis on kinetics of tap water dechlorination found that it takes several minutes for a dechlorinator to react with chlorine" - do you have a reference for that statement? I would love to read it, as previous papers that I read yrs ago stated the reaction time was typically considered instantaneous. I'm guessing that this students thesis had nothing to do with aquariums, and fish?

I would expect that how long it takes to react with chlorine in an aquarium setting could be dependent on several factors, such as the type or form of dechlorinator being used, the amount of dechlorinator being used, the level (ppm) of chlorine in the tap water, the volume of tap water being treated, the pH of the water being dechlorinated, the temperature of the water, etc.

Another factor most likely not found in the students thesis is that in an aquarium setting, residual free chlorine is also consumed by the oxidation of organic compounds present in the aquarium water. I suspect that would be a major factor in the dechlorination process, especially in mature systems.

 

[squint]

It's "Kinetics of Tap Water Dechlorination and Aquatic Health Impacts of Selected Dechlorination Chemicals" by Bhagya N. Weerasinghe. Its focus is on the dechlorination of tap water before discharge by treatment plants so it doesn't harm aquatic organisms. These studies do factor in chlorine demand. As I understand it, chloramine is less reactive than chlorine so you can't rely on organics in the tank to react to it. Chlorine may in fact react to ammonia in the tank and form chloramine, making things worse.

Also read the ClorAm-X patent (4,666,610) where Kuhns gives pretty much the same numbers (several minutes for chlorine) but also has data for chloramine and ammonia.

All the reactions seem to be second order reactions and this is where I think Prime may have trouble. Prime dechlorinates only about 24% more per volume than ClorAm-X-based dechlorinators but is dosed 5X less. If the reaction rate is dosage dependent then Prime could take a good bit longer.

 

[RD.]

I've spoken with both John Kuhns from Aquascience Research Group, and Dr. Greg Morin from Seachem, and picked both of their brains on as much as I can over the years. I'm no chemist, long ways off, but according to the tests that I have performed in my own tanks, with tap water that is treated with chloramine @ 2 pmm, the reaction time is pretty much instantaneously. With products such as Seachem Safe, the chlorine/ammonia bond is broken on contact with the dechlorinator, the chlorine is then reduced to harmless chloride and the ammonia is then bound until it is utilized within the biological filtration. Unless you raise your pH to 12 it will not release the ammonia back.
This has always been my understanding. I add Safe before I begin to refill my tanks, and then gradually in stages as the tank fills. IMO adding product in stages over a 30-60 min tank refill reduces any chance of the dechlorinator being spent on reducing oxygen, vs chlorine and/or ammonia.

So if you follow the process, the moment that the chlorine/ammonia bond is broken, any residual free chlorine is also being consumed by the oxidation of organic compounds present in the aquarium water. If one wants to test aquarium products, they need to be tested in aquarium settings, not just in test tubes.

 

[squint]

How did you perform your tests?

Did you ask Kuhns specifically about what he wrote in his patent?

The thesis abstract states:

The kinetics of seven dechlorination agents (DA) was studied to identify the efficacy of dechlorination under variable dosage, mixing (periodic/continuous), and pH conditions (6.5 - 8.6 and/or >9). Dechlorination reactions at lx stoichiometric dosage (mg DA/ mg CI2) of the DAs are rapid in most cases, but not instantaneous and in some cases needed more than stoichiometric dosage to ensure a near zero residual level (0.02 mg/L total residual chlorine, as required by CEPA (1999)). Dechlorination kinetic analysis revealed reactions were either pseudo-first or zero order with respect to total chlorine concentration in solution at the l0x stoichiometric dosage and second order overall at 2 - 4x stoichiometric dosages.

http://www.seachem.com/support/forums/forum/general-discussion/2431-questions-about-prime

This is what Seachem has to say about releasing ammonia:

Thanks for your questions. You do understand correctly that Prime removes chlorine and chloramines; and it detoxifies ammonia, nitrites, and nitrates. It detoxifies these nitrogenous compounds by binding them into a non-toxic form. They stay bound for about 24-48 hours and then are released back into their original form.