[mix_boom]

I've been doing this experiment, calculating BOD of waste water.
But, it seems that it always failed.
I put in 1 mL of MnSO₄ solution, 1 ml of NaOH+KI into the water sample. Then, white precipitation was formed...
Then, I put in 1 mL of sulphate acid (from 50 mL pure sulphate acid and 460 mL distilled water).
If oxygen exists, the colour of solution should be yellowish...but it never was in my experiment...

I stick to this procedure: http://www.epa.gov/greatlakes/monitoring/sop/chapter_5/LG501.pdf

When I read the procedure, it is said that when the NaOH+KI solution is added some sulphuric acid and starch indicator, there should be no color... But then blue color was seen!
In fact, once I tried to do the experiment without any water sample... ....just using the reagents... And there comes the blue, which should NOT happen...

A) Do anyone knows all reactions which are involved in this experiment?
B) would you please put out the possible mistakes I've done?

Thanks...!