**www.koi-unleashed.co.uk**

Have you ever thought of the virtues
of checking your test kits for accuracy? well maybe you should, not only will
this show you if they are past their sell by date and useless , but in the
past i have found some test kits leave a lot to be desired for accuracy.

If you know the error in
the kit, this will give you the luxury of allowing for that error when testing
your water parameters, this can only be a good thing.

By Spike Cover, April 7, 2003

** **

Precision – reproducibility

Sensitivity – smallest increment that can be measured - resolution

Accuracy – variance from actual

**Stock solution – ammonia test **

Prepared by
mixing 3.14 grams of ammonium chloride (NH_{4}Cl) into1 liter of
distilled water – the 3.14 grams was arrived at by taking the atomic weights of
the chemical and then determining how much of the ammonium chloride is required
to yield the desired amount of ammonia (NH_{3}).

The relevant numbers are (ref: periodic chart):

N = nitrogen, atomic weight of 14.0067

H = hydrogen, atomic weight of 1.0079

Cl = chlorine, atomic weight of 35.453

So NH_{4}Cl
has an atomic weight of 14.0067 + 4x1.0079 + 35.453 = 53.49

And NH_{3}
has an atomic weight of 14.0067 + 3x 1.0079 = 17.03

If we desire
1000 ppm of NH_{3}, we need 1000 mg of NH_{3} per 1 liter of
water

But since we
have NH_{4}Cl and not NH_{3}, we will need 53.49/17.03 x 1000
mg = 3141 mg of NH_{4}Cl to yield 1000 mg of NH_{3}, or 3.141 g
of NH_{4}Cl

If we desire to
make up 1 liter of ‘stock solution,’ we will need to add 3.141 g NH_{4}Cl
or 3.14 g when rounded to two decimal places, i.e., this is the amount of NH_{4}Cl
that would be added to 1 liters of distilled water to make a 1000 ppm solution
of NH_{3}.

**Exercise** -
Test ammonia kit

Using the pre-made stock solution of 1000 ppm ammonia, make diluted solutions to test your ammonia test kit.

Example: take 1 ml of the stock
solution and add to 1 liter of distilled water to make 1 ppm or 1 mg/l, stock
solution of NH_{4}Cl,

2 ml of stock added would make 2 ppm or 2 mg/l

0.5 ml to 1 liter would make 0 .5 ppm or 0.5 mg/l, etc:

Then fill the test tube of your kit to the kits required level and test

Use at least 4 data points (5 would be better), including zero ammonia, to generate a curve of actual vs. readings to show the spectrum of error, (use graph paper) for your (individual) ammonia test kit. Make sure you span the manufacturer’s stated range of your kit.

On your graph, label the x and y axes, actual and reading, respectively and show values in ppm or mg/l which ever you prefer.

**Additional tests for NO _{2} and NO_{3}** - using sodium nitrite (NaNO

**Stock solution – nitrite test**, the
relevant numbers are (ref: periodic chart):

Na = sodium, atomic weight of 22.9898

N = nitrogen, atomic weight of 14. 0067

O = oxygen, atomic weight of 15.9994

K = potassium, atomic weight of 39.0983

Sodium nitrite, (NaNO_{2}) has an atomic weight of 22.98978
+ 14.0067 + 2x 15.9994 = 31.9988. = NaNO_{2} atomic weight of = 68.9953

Nitrite alone (NO_{2}), has an atomic weight of 14.0067 +
(2X 15.9994) = 46.0055

If we desire 1000 ppm of NO_{2}, we need 1000 mg of NO_{2} per
1 per liter of water.

But since we have NaNO_{2} and not NO_{2}, we will need,
68.9953 / 46.0055 x 1000 mg = 1482.1755 mg of NaNO_{2} to yield 1000 mg
of NO_{2}.

If we desire to
make up 1 liters of ‘stock nitrite solution,’ we will need to add 1.48 g of
sodium nitrite, when rounded to two decimal places, i.e., this is the amount of
NaNO_{2} that would be added to 1 liters of distilled water to make a
1000 ppm solution of NO_{2}.

**Stock solution – nitrate test,** the
relevant numbers are (ref: periodic chart):

K= potassium, atomic weight of 39.0983

N= nitrogen, atomic weight of 14.0067

O = oxygen, atomic weight of 15.9994

Potassium nitrate (KNO_{3)} has an atomic weight 39.0983
+14.0067 + (3X 15.9994) = 101.1032.

Nitrate alone (NO_{3)} has an atomic weight of 14.0067 + (3X
15.9994) = 62.0049

If we desire 1000 PPM of NO_{3}, we need 1000 mg of NO_{3} per
1 liter of water.

But since we have KNO_{3} and not NO_{3}, we will
need 101.1032 / 62.0049 x 1000 mg =
1630 mg of KNO_{3} to yield 1000 mg of NO_{3}.

If we desire to
make up 1 liters of ‘stock nitrate solution,’ we will need to add 1.63 g of
sodium nitrite, when rounded to two decimal places, i.e., this is the amount
of KNO_{3} that would be added to 1 liters of distilled water to make
a 1000 ppm solution of NO_{3}.

**pH**

Sodium hydrogen carbonate; sodium
acid carbonate; baking soda; bicarbonate of soda

Molecular Weight: 84.01

NaHCO3

Solubility: 7.8g/100g water @
18C (64F).

pH: 8.3 (0.1 molar @ 25C (77F))

Add 7.8 gm of Sodium Bicarbonate to 100ml of tap water this should settle to give a pH of 8.3-8.4 check your test kit using this buffered solution.