Extracting potassium nitrate crystals from NPK fertilizer with a composition of 20-20-20 is technically possible, but it is not practical. The fertilizer may not contain potassium nitrate specifically, as it primarily includes nitrogen and potassium in different forms. Purchasing potassium nitrate directly is a simpler and more efficient solution. Additionally, there are regulatory considerations regarding the purchase of certain compounds, which may influence the decision to extract rather than buy.