Include Sulfur?

By leaving out the sulfur there will be a "degree of freedom" in solving the problem. This will make it more likely that we will be able to match the NPK (Nitrogen Phosphorus Potassium) exactly. NPK is more important for plants than sulfur. We must give NPK priority over sulfur.

Instructions that describe how to perform hydroponic calculations usually allow sulfur to "go along for the ride". If you use magnesium sulfate to supply magnesium then you should have no problems with sulfur.

Sulfur appears in many places especially in the micronutrients (copper sulfate, zinc sulfate, etc) thus further compounding the problem of finding an answer.

My calculator treats all elements equally. My calculator does not discriminate among the various elements. For example, a formula that has an error of 2% in nitrogen and an error of 25% in copper is better than a formula with an error of 25% in nitrogen and 2% in copper.

Good Tip

If you plan to include sulfur in the calculations then you can "remove the sulfur" from micronutrient salts such as manganese sulfate, zinc sulfate, and copper sulfate.

For example, instead of specifying Copper Sulfate as 25.4% copper and 12.8% sulfur, you can specify Copper Sulfate as 25.4% copper only. The amount of copper needed is typically below 0.1 ppm. It makes no sense to include the amount of sulfur contributed by the copper sulfate in the calculations. Doing so can lead to having large errors in the NPK ratios.

An extreme example is Ammonium Molybdate. Here you have molybdenum, a micronutrient, competing directly with nitrogen! It will be best to specify Ammonium Molybdate as 54.3% molybdenum and zero percent nitrogen. The same logic will apply to nitrate salts such as zinc nitrate, copper nitrate, etc.

I decided to include a sulfur option after receiving an email inquiring as to why sulfur was missing from my calculator.