My name is Tara and this is my
partner Lashana. We are going to tell you how to do the dissolved oxygen test.
First you need to fill the water sample jar to the 20 mL line. Then you add
eight drops of Manganous Sulfate Solution. Then you need to add eight drops of
Alkaline Potassium Iodide Azide. After you add that stuff there should be white
floaty stuff in the water sample. That should settle in the bottom or as low as
it is going to go because a lot of times it doesn’t all settle in the bottom
of the container. When it has settled you need to add eight drops of Sulfuric
Acid. Then you need to fill the titrator and add drops of Sodium Thiosulfate
until your sample turns a pale yellow color. Sometimes that takes more than one
full titrator full but usually never more than two. Then you add eight drops of
Starch Indicator. That turns the sample a dark blue or purple color. Then once
again you fill the titrator and add drops of Sodium Thiosulflate one at a time
until it turns perfectly clear. While doing this step you need to mix the sample
up after every drop or you wont get a clear reading. When your sample is clear
you need to look at the titrator and count each line as one and how much is
still in there is how many ppm’s you got on that particular test. After you do
that it is really important that you get the temperature of the water because
you have to do the percent saturation. To do this you need the chart and you
find the temperature and the amount of ppm then draw a line from the temp to the
amount of ppm and it crosses over the percent saturation line and that is the
percent saturation.
This is an important test because if the Dissolved Oxygen level is to low
all the fish will leave or die because they won’t stay were they cant breath.
If it is to high then plants and algae will start growing to the point that they
will get out of control.