Understanding test kit chemistry for the aquarist.

 

Introduction:

 

Ever wonder exactly what happens when you add the little drops to the little test tubes? Or just what condition does your water conditioner leave your water in? Well, I have too, and the following article is an attempt at de-mystifying water conditioners and aquarium test kits. Unfortunately, Aquarium Pharmaceuticals does not list the test ingredients on the bottles or in the instruction book. The only response to my E-mail inquiries for the ingredients, and a description of the chemistry, was that the MSDS data was available on the website. I was able to find the formulas and reaction summaries for water tests offered by the Hach Company. Since the Hach tests seemed to have the same color endpoints as the Aquarium Pharmaceuticals tests, and some of the ingredients on the Aquarium Pharmaceuticals MSDS were the same or similar, I inferred that Aquarium Pharmaceuticals would not go through the trouble of inventing their own tests, but would use established, reliable methods already in existence, albeit modified for the home aquarium use. I hope I was not too far off the mark. The information about Amquel and Ammo-lock were from the manufacturers websites. Any claims made by either party about their own product or their competitors product should be tempered by the knowledge that they are in competition with each other. It is best to use the Salicylate based ammonia test (two bottle test) since it has been described to me as more accurate, and you won’t get fooled into thinking you have really high ammonia levels with a Nessler Reagent test, if some Amquel or similar product got in your tank. I could not find any reference about Ammo-lock and the Nessler reagents on the internet, but was told in a post on AquariumAdvice.com that there is a warning about interference with Nessler reagents on the bottle. I was not  trying to foster mistrust of your test results by including a list of the many metals and other chemicals that can interfere with the tests. I listed them so that someone who had a known high level contaminant in their water would know to look into the subject further. I hope this article will make the water conditioners and the nitrogen tests less mysterious for you. While this will not make you an analytic chemists, at least you can have some basic idea about something you will be doing frequently.

 

Water Treatments / Conditioners:

 

Thiosulfate

Sodium Thiosulfate and dechlorination:

 

Chlorine is present in the water as Hypochlorite: HOCL . Free Chlorine gas (Cl2) can diffuse out of the water and is

in balance with hypochlorite.

 

 

 Cl2 + H20   a HOCl + H + Cl   and      HOCl  a H + OCl

 

 

Aeration greatly speeds the removal of chlorine and hypochlorite, as do dechlorinators. Thiosulfate ion (S2O32- ) is

 

used to remove chlorine (hypochlorite) from water.

 

 

 HOCl + 2 S2O32-      a    Cl- + S4O62- + OH-

 

 

 

 

AmQuel

 

The active ingredient in AmQuel is known chemically as sodium hydroxymethanesulfonate:

     

       HOCH2SO3Na.

 

The hydroxymethane- end of the molecule (HOCH2) reacts with ammonia to form a non-toxic, stable water-soluble

substance which is acted upon by the bacteria in biological filtration. This reaction effectively removes the toxic ammonia from solution. Even in water of low pH (<7.0), the above reaction proceeds to completion. This is because even at pH’s below 7.0, there is always some "free" ammonia (NH3) and the AmQuel will scavenge it from the water. This

is why AmQuel works faster at higher pH's and in saline waters, since a higher percentage of the ammonia is in the NH3 state. The substance formed is stable, and testing has shown that even in an aquarium or pond without a biological filter, the ammonia is not released back into the water. Also, unreacted AmQuel is stable, and unless removed with water changes or granular activated carbon, it will be available to react with ammonia until it is exhausted in the water to which it was added. Excess AmQuel can be added to the water to act at a later date without adverse effects on the fish or invertebrates.

 

The sulfanate end (SO3) of the Amquel molecule reacts with both free-available chlorine, know properly as

hypochlorites, and combined -available chlorine (chloramines). In the first instance, nothing more than harmless chloride ions are produced, and in the latter instance chloride ions are formed  and the freed ammonia instantly reacts with the hydroxyl-methane end of the molecule.

 

ammonia                 AmQuel                         aminomethanesulfonate            water
  NH3         +        HOCH2SO3-       ==>        H2NCH2SO3-          +       H2O 
 
 
 

This information is from Kordon’s website at http://www.novalek.com/kordon.htm  

Amquel will cause the Nessler ammonia test to turn dark brown, indicating high ammonia levels. Thus, do not use Nessler ammonia tests after Amquel. Amquel will indicate low oxygen levels with oxygen test kit that uses Winkler reagents, so don’t use this test after Amquel.

 

Ammo-Lock
 

Aquarium Pharmaceuticals  does not list the contents of its dechlorinator, or of Ammo-lock, but I believe it to be of a similar principle as Amquel. The MSDS states that there is a “trade secret” aliphatic amine and some sodium thiosulfate. They claim that the Ammo-lock will not affect the salicylate test for ammonia, and that ammonia bound to Ammo-lock will still show up on the salicylate test. They imply that with their competitors products, ammonia won’t show up on a salicylate test, which hides the ammonia and deceives the aquarist (remember, they are in competition!).

 

Bio-Safe

 

Bio-Safe, by Marineland Labs, contains Sodium Hydroxymethane sulfinic acid. It causes false high readings with Nessler reagents, but is “compatible” with salicylate tests. I suspect this is the generic of Amquel, or close enough chemically to be considered the same. If so, even if the Bio-safe is compatible with a salicylate test, perhaps the ammonia bound to the Bio-safe might not show up on a salicylate test? Or am I just a marketing victim of Aquarium Pharmaceuticals? (see above).

 

Ammonia Testing:

Salicylate testing for ammonia

 

This analytical method is based upon the treatment of ammonia compounds in a seawater or freshwater sample with chlorine to produce monochloramine.  The monochloramine is reacted with salicylate to form 5-aminosalicylate.  Sodium nitroprusside acts as a catalyst for the oxidiation of 5-aminosalicylate to indosalicylate, a blue colored compound.  The blue color is masked by the yellow color from excess reagent to give a final color of green. This color change is proportional to the amount of ammonia in the sample and can be determined using the indicator card.

 

 

Interference: (not a complete list, where interference levels are given they are for the Hach Co test, and might not appy to Aquarium Pharmaceuticals)

 

Extremely hard water (CaCo3 >1000ppm), and extremely high nitrite (>12ppm) and nitrate(>100ppm) levels can effect the test, as would high Iron, Calcium, Phosphate,Sulfate, Magnesium and Sulfide. Food particles will cause the test to turn green also.

 

So, if you have monochloramine in your water, it should turn color and detect the monochloramine? I have not seen this written, but it can be inferred. A way of testing your tap water for monochloramine!

 

Aquarium pharmaceuticals does not list the ingredients to the ammonia test, but many of the above ingredients are on the MSDS for the test. I believe it to be the same.

 

Nesslers Reagent:

 

Nesslers Reagent is Mercury Iodide in a Potassium Iodide and Potassium Hydroxide solution.    KI + HgI2  or K2HgI4

In the presence of ammonia (NH3) Iodide is released which turns the solution brown. If the sample has been treated with Amquel, the Nesslers reagent will turn dark brown, invalidating the test. I believe Nessler tests are a one bottle test, while salicylate tests are two bottle tests.

 

 Nitrite Testing:

Diazotization Method

 

Nitrite ions react with sulfanilic acid to from an intermediate diazonium salt. This reacts with chromotropic acid to produce a red-orange complex directly proportional to the amount of nitrite present.

 

 

Another method uses the same sulfanilic acid, but instead of chromotropic acid the diazonium salt reacts with 1-naphthylamine sulfonic acid to form a different red-colored solution. This may be what is in the Aquarium Pharmaceuticals kit? Since the Nitrate test has a common pathway with the nitrite test, they may have chosen the second indicator to avoid confusion? (see Nitrate testing below)

 

Interferences: (not a complete list, where interference levels are given they are for the Hach Co test, and might not appy to Aquarium Pharmaceuticals)

 

Very high levels of nitrate (>100 ppm) since some of the abundant nitrate will convert to nitrite and register on the test. Ferric Ions, Ferrous Ions, Lead Ions, Mercurous Ions, Cupric ions.

 

Aquarium Pharmaceuticals does not list the ingredients to the nitrite test on the bottle or the instruction sheet, but sulfanilic acid is listed on the tests MSDS sheet, so I believe they are the same.

 

 Nitrate Testing:

Reduction method:

 

Cadmium metal (says Hach), or perhaps Hydrazine (says TheKrib.com), or maybe even Sodium Bisulfite (says the AP MSDS sheet), is used to reduce nitrates to nitrites. Nitrite ions react with sulfanilic acid to produce an intermediate diazonium salt, like in the nitrite test. The diazonium salt then forms a red-orange complex with chromotropic acid. The reaction after the cadmium, hydrazine, or bisulfite (or whatever it is!) reduction is the same as shown in nitrite testing above. Thus, the test actually measures nitrate by the amount of nitrite it can be converted into. 

 

 Interference: (not a complete list, where interference levels are given they are for the Hach Co test, and might not appy to Aquarium Pharmaceuticals)

 

Calcium (100ppm), Chloride (>100ppm cause low results) which means your saltwater test will yield too high a result in freshwater (SW kit calibrated higher to compensate for the lowering effect of higher chloride), Ferric ion

Nitrite – since the test measures nitrite, any nitrite present will add to the observed nitrate level. Since your nitrite should be near zero, this usually doesn’t matter. Also, since your Nitrate kit is testing for greater than 5ppm, you wouldn’t notice the nitrite effect unless it gets very high, at which point your tank is really out of whack and nitrates are your last concern. Nonetheless, if your cycle seems stalled because you have high nitrite and and nitrate that isn’t changing, perhaps the nitrate you thought you had was really mostly nitrite.

 

Once again, Aquarium Pharmaceuticals does not list the ingredients to the nitrate test, but sulfanilamide is listed as an ingredient on the MSDS, so I believe it is the same or very similar.