The problem: The milliliters of stock solution to add is ALWAYS too small.

The reason: A misconception that the ratio of grams compound/mL of water is important; this is entirely useless. Rather, what is important is the ratio of

*Example:*

**grams compound/mL solution**150g of KNO3 in 250mL of water. "Fertilator" says that if we want 10ppm of nitrate in 50 gallons of water, we should add 5.15mL of stock solution. This is wrong and adding 5.15mL will only achieve 6.0ppm of nitrate. That is 40% error!

Here is where the misconception comes in: We think that since there is 150g KNO3 in 250mL of water, there is 0.60g/mL in our stock solution (150/250=0.60). Wrong! We cannot forget that compounds themselves have volumes, and add volume to the solution. 150g of KNO3 has a volume of about 165mL, which when added to 250mL of water give us a total solution volume of roughly 415mL. So each milliliter of solution has 0.39g KNO3 (not 0.60g). It is important to realize that the volume of solution is important, not volume of water.

Going back to our case senario. When we change the number in the "volume water" from 250mL to the acutal 415mL that is important, the real amount of stock solution to add is 8.84mL, not 5.15mL.

To correct this the answer is very simple. Instead of the field being read, "Amount of water to mix with," change it to: "Total volume of solution."

Hope this helps! I can explain anything if it was confusing.

-Chris