# Mg+K+Fe=no NO3???



## Ravenswing (15 Dec 2012)

Sounds impossible, or does it?

A hobbyist fellow of mine has noticed that that adding Fe, K and Mg to a water with NO3 (tap 12,5mg/l), NO3 disappears totally. He has repeated this few times in a bucket with the same result. How come?  He has been using JBL drop tests so I think they should be accurate.


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## Nathaniel Whiteside (15 Dec 2012)

Isn't this why we dose Marcos (NPK) and Micros ( Fe etc.) on different days? As the Fe reacts with the macro, forming another compound. Thus no No3 being present?


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## Arana (15 Dec 2012)

I would not trust any hobbiest test kits to give you an accurate result


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## Ravenswing (15 Dec 2012)

Im pretty sure there is something wrong with his test kit but not being an expert on chemistry, I d like to hear a second opinion about this phenomenon I was described.


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## ceg4048 (15 Dec 2012)

I'm pretty sure there is something wrong with your friend if he thinks using test kits will help him grow better plants. He needs to throw his test kits in the bin and somehow find a way to carry on with his life.   

Send this message to your friend:
"The Matrix has you Neo.."





Cheers,


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## nayr88 (15 Dec 2012)




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## Ravenswing (17 Dec 2012)

ceg4048 said:
			
		

> I'm pretty sure there is something wrong with your friend if he thinks using test kits will help him grow better plants. He needs to throw his test kits in the bin and somehow find a way to carry on with his life.



Oh no, he`s just new with planted tanks and was a bit confused with this NO3-result=0mg/l after adding it. But you are right when it comes to growing plants with tests. I recommend to use your own eyes being the best test kit but people just feel soooooooo good to use them and make everything messy with them not understanding that they are just tools, not the answer. Or the target.


Thank you all for your replies.


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## dw1305 (19 Dec 2012)

Hi all,
There is an explanation for this, and it is one of the reasons why test kits, or even ion selective electrodes, aren't particularly useful for testing for nitrate (NO3-).

When you add cations like Mg++, K+ or Fe+++ you are also adding an anion (from the dissolution of the salt). These anions may be ones that we want, like PO4--- and NO3-, or they may be ions like C-, SO4--, HCO3- that will be already present at the levels required for plant growth.

When we add other ions we have 2 possibilities, one is that one of the added cations will combine with nitrates present, and form new insoluble compound(s) that precipitate out of solution. This happens commonly with ortho-phosphate ions, because the majority of phosphate compounds (iron phosphate, calcium phosphate etc) are insoluble. We can however discount this, because in practical terms all nitrates are soluble in water.

It does leave us with the option that the nitrate test was actually always measuring interference of another ion, and that this ion has formed a new compound which is insoluble, and no longer causing the "NO3" reading.

It is more likely that there were NO3- ions present, and they are still there, but that the test kit is now not registering them. The reason for this is as simple as interference from other anions. The sulphate, chloride and carbonate ions etc. we have added are interfering with the measurement of the nitrate ions. This is by far the most likely option, and one of the difficulties in water testing for nitrate.

This interference effects both colormetric methods and ion selective electrodes, and is one of the reasons that Freshwater Biologists use BOD and biotic indexes to estimate pollution in streams and lakes, rather than relying on analytical methods.

cheers Darrel


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## Ravenswing (19 Dec 2012)

Hi Darren and thank you very much for your responce, this really helps to understand what might have happend. I wonder why this phenomenon is so rare? There are thousands of hobbyists adding all these salts to their tanks but Iv neverever heard/read this "NO3 disapearing" happend before!


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## Nathaniel Whiteside (19 Dec 2012)

Whitey89 said:


> Isn't this why we dose Marcos (NPK) and Micros ( Fe etc.) on different days? As the Fe reacts with the macro, forming another compound. Thus no No3 being present?






dw1305 said:


> Hi all,
> There is an explanation for this, and it is one of the reasons why test kits, or even ion selective electrodes, aren't particularly useful for testing for nitrate (NO3-).
> 
> When you add cations like Mg++, K+ or Fe+++ you are also adding an anion (from the dissolution of the salt). These anions may be ones that we want, like PO4--- and NO3-, or they may be ions like C-, SO4--, HCO3- that will be already present at the levels required for plant growth.
> ...






Yeah Darrel,
I just said that


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## plantbrain (19 Dec 2012)

We use a standard reference when testing water samples in research. Hobbyists can/should do this step as well.

Then you can know whether the test method is correct. Most hobbyists are simply unaware of how to test properly, and assume the test kits are accurate and precise.
They are NOT.

Being upset at this revelation is not warranted really.
Knowledge is the death of ignorance


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## dw1305 (20 Dec 2012)

Hi all,


> Isn't this why we dose Marcos (NPK) and Micros ( Fe etc.) on different days? As the Fe reacts with the macro, forming another compound. Thus no No3 being present? ..........Yeah Darrel, I just said that


You did, that is the reason and if we had been talking about phosphate (PO4---) you would have been right on the money. Because all nitrates go in to solution it means, unfortunately, that we can't use precipitation as a technique for measuring them.


> We use a standard reference when testing water samples in research. Hobbyists can/should do this step as well.


 As Tom says there are standard methods for water testing, and there are also protocols in terms of how many samples you need to take, and how you should report those values (usually in terms of a mean and confidence interval, assuming the sample data is "normally distributed"). The reference methods for the US are available via the web. US EPA: <Clean Water Act Analytical Methods | CWA Methods | US EPA>, inorganic anions <http://water.epa.gov/scitech/methods/cwa/bioindicators/upload/2007_07_10_methods_method_300_0.pdf>.

Even if we don't have access to the equipment and reagents needed for the standard analysis, we can make use of the test kit we do have to give us a much closer estimate of the likely NO3 value, as long as we have access to a suitable salt, like potassium nitrate (KNO3) electronic scales and some RO water. We can use scales, because 1ml of H2O weighs 1g (at 20oC), meaning that we don't need to be able to measure volumes accurately.

Using the dosing calculator on "James' Planted Tank" <James' Planted Tank - Dosing Calculator>, we can make up a stock solution, which when diluted will give us a solution containing ~200ppm NO3. (To do this dissolve 3.36g KNO3 in 250ml of H2O to make a "stock solution", when 25ml of the stock solution is added to a litre of tank water (in a separate container, not in the tank) we have added 200ppm NO3).
All we need to do then is dilute (serial dilution) the 200ppm stock solution with RO water to give us a range of known added NO3 values.

If you split the 200ppm stock solution 50:50 with RO water, you've added 100 ppm NO3,
If you go 1:3 200ppm stock:water, we have added 50ppm NO3,
1:9 20ppm
1:19 10ppm etc.
Once we have a range of "added values", we can test each of the solutions with out test kit, and construct a standard curve. We can then repeat the process, but using entirely RO water to make our 200ppm stock solution, that we then serially dilute to give us our range of true NO3 values.

Hopefully our tank value will lie somewhere along our curves, and we will get an estimate of the "true" NO3 value in out tank water, it will only be an estimate, because we will have diluted the other anions in the tank water with RO etc.

Is it worth doing this? in my opinion not in a million years, but if we want to use a test kit (or even an ion selective electrode) to get an at least semi-quantitative value, it is the sort of procedure we need to follow.

It is possible that one day there will be cheap off-the shelf meters and kits that will give you quick accurate readings over a range of conditions (like a conductivity meter will), but I'm not holding my breathe.

cheers Darrel


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## ian_m (20 Dec 2012)

We used to do some form of chemical etching, a long while ago at work, for printed front panels and had to use test kits to verify the tap water used to make solutions and/or washing before starting. One was a chloride test kit (I think) and if any chloride was present there was no point in doing further tests (nitrate & metals I think) as presence of chloride would affect the other tests. Sound similar to aquatic test kits, absolutely fine if you wanted to measure say the nitrate dissolved in distilled water, but useless to measure the nitrate levels in water containing plenty of other soluble salts. I have a feeling that all the test kits were rendered useless by presence of arsenic and sulphites as well, so fine for tap water (hopefully ) but no good for contaminated water testing.


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## dw1305 (20 Dec 2012)

Hi all,


> One was a chloride test kit (I think) and if any chloride was present there was no point in doing further tests (nitrate & metals I think) as presence of chloride would affect the other tests. Sound similar to aquatic test kits, absolutely fine if you wanted to measure say the nitrate dissolved in distilled water, but useless to measure the nitrate levels in water containing plenty of other soluble salts.


Ian that is exactly it, you get a most interference from chloride and nitrite ions and variable amounts from the other anions.

If you have distilled water and add KNO3, the kits are accurate and the values repeatable. Even in the case of sea water you have an extremely large known amount of Cl- ions (18.8 g/L is a typical seawater chloride level), and you can use this to your advantage, but if you don't have a known value in your sample (like in freshwater) you're stuffed. You also get interference from any dissolved organic matter.

You can get a break-down of the strengths and weaknesses of the methods from Hach in the US, if you type "Hach & Cadmium Reduction Method", "Chromotropic Acid Method" or "Nitrate Ion-Selective Electrode" you can find the application for different monitoring techniques. 

cheers Darrel


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## Martin cape (22 Dec 2012)

I dont use any test kits, I work in a lab so can test everthing there lol


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## dw1305 (22 Dec 2012)

Hi all,


> I dont use any test kits, I work in a lab so can test everthing there lol


 Useful to know. We don't test many water samples now, so he can't add samples to the ends of runs etc.
Do you do BOD testing?

cheers Darrel


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## Martin cape (22 Dec 2012)

Never heard of BOD. Most of our stuff is pond water samples. Using an Ion Chromatography system. Helped when I cycled my tank lol


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## plantbrain (25 Dec 2012)

You can do chemical oxygen demand much easier, some places require by law to do only Biological O2 Demand.
COD will give you a pretty good indication.  BOD takes much longer, so there's a delay of a day or two for reporting.
The hach BOD method is one of the easier ones to use. Not to mention the probes are easier than the other brands.

In support of Darren's comments, NO3 is not the easiest anion to measure. Probes and standards can be used, but you have to treat the samples for interfering ions. Cannot do this practically in an aquarium. Well, you could, but then you'd need an autosampler and another few $$$$$$.
Many NO3 test kits have a wide error ranges, many users and few standards to check. All things that cause issues. If you have a decent standard curve with whatever method chosen, then you should be fine.

I think the main test most of the more advance folks use: plant and fish/livestock observations. They know if there's something amiss.
Ferts? Even easier. Water change + dose EI ranges of ferts= non limiting levels.

This is like your standard curve for your test using the Ion Chromatography. But much simpler and faster.
Then observe post dosing and keep doing the method.

Another way is to use rich sediments, but sediments only bind NH4, not NO3(in any significant amount), which is why you have NO3 is tap and other water supplies. NH4 is easily removed or mineralized to NO3.
Sediment swill bind NH4, but......bacteria attack and mineralize NH4 rapidly. But ADA AS might last roughly 1 year, maybe more, maybe less as a sole source with fish waste for most CO2 enriched tanks.
Fish (can) add a decent source also.

BGA is common in NO3 poor planted tanks. So if you miss the plant cues, there's always algae waiting for the worse issues


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## dw1305 (29 Dec 2012)

Hi all,


> Using an Ion Chromatography system


 Now that is very interesting, we have an HPLC and a GC, but neither of those are of much use to me, an ion-exchange chromatography system (IC/IEC) would be more useful (it produces peaks for all the charged particles (ions) in the water as the stationary phase of the column retains the differing anions in the analyte for differing times), although you would need both anion and cation exchange columns to cover all the ions we are interested in.

Like Tom says the problem with *other methods* of NO3- measurement is that other anions interfere with the NO3- measurement, which takes us right back to what the OP found originally. If he had access to an IEC system, the computer software to control it, a suitable column and active phase carrier he could have got a more accurate estimation.

Both BOD and COD are different in that they aren't quantitative tests, but provide an estimate of the potential demand for oxygen, which is however a pretty good measure of the organic pollution of a water sample. The advantage that BOD offers over COD is that it is much more sensitive, you can think of COD as giving you a ball-park figure, and BOD as adding all the decimal places.

For rivers and streams, if you have a measure of BOD and carbonate hardness, you don't really need any other analytical measurements to give you an idea of water quality and likely biota. When you sample the invertebrate biota, if there is a big discrepancy between the species assemblage you would expect, based upon the water quality, and the species you find (or more importantly don't find), you can be pretty sure there has been a pollution incident. If any-one is interested there are more details here: <RBMS - Title and Index to web pages>

To give some figures a really clean river will give a 5-day BOD below 1 mg/L. Most "clean" rivers in the UK rivers will have a BOD value of between 2 & 10 mg/L. Treated sewage about 20 mg/L and raw sewage anywhere from 200mg/L (winter) to 1000mg/l (summer).

Even though we can't measure BOD, we can still make use of it as a concept. When I add something to the tank I think of it in terms of BOD. If you feed your fish a protein or sugar rich food you've raised the BOD, because you've provided a substrate for bacteria, and you've increased the ammonia production of the fishes metabolism. Both of these activities lead to increased oxygen demand.

If you add fertilisers the situation is more complicated, you potentially increase the BOD, because nutrients become non-limiting in terms of plant growth and plants are leaky organisms, but much of that increased metabolism is incorporated into new plant tissue. Photosynthetic organisms also differ from all other forms of life because they are net oxygen producers. EI and the Duckweed index both make use of healthy plant growth to maintain water quality, but EI is a much more intensive system, where inputs and plant growth rates are much higher, and regular large water changes, maintenance and plant pruning remove organic compounds from the system.

cheers Darrel


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## Martin cape (29 Dec 2012)

We have some chemists in the building lol.

Yea the one I use is HPLC with the ion exchange columns. It's really good at giving me the accurate readings for 6 anions (even though I don't need some). 

Another lab analyses COD, I'm not familiar with that.


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## dw1305 (3 Jan 2013)

Hi all,


> We have some chemists in the building lol


 I'm not really a chemist, I only know about the bits of chemistry I've needed to know for the work that comes in the lab.

COD is more fully described in this thread: <Guppies strange behaviour | UK Aquatic Plant Society>.

cheers Darrel


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