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I am quite new to hydroponics so forgive my ignorance :)

I am planning to make a simple DWC set up (for tomatoes) and was wondering if I could use a water soluble fertilizer (20-20-20 with Mg Fe Cu etc.) as the nutrient solution since (according to the label) it can provide NPK with other macro and micro nutrients for plants that grow in soil-less environment or should I only use nutrient solutions made especially for hydroponics? How different are they?

Thank you!

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  • Look up magnesium phosphate. It is virtually insoluble. Don't know how the hydroponics for deal with this, but I suspect pulse feeding.
    – Wayfaring Stranger
    Jan 22, 2020 at 1:56
  • @WayfaringStranger Magnesium sulfate (epsom salt) is common for hydroponics.
    – user1850479
    Jan 22, 2020 at 3:42
  • Yes, I know. It's the Mg plus phosphate That's missing from most soluble fertilizers. The problem is tractable, you just have to think it through some.
    – Wayfaring Stranger
    Jan 22, 2020 at 4:42

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I am planning to make a simple DWC set up (for tomatoes) and was wondering if I could use a water soluble fertilizer (20-20-20 with Mg Fe Cu etc.)

It depends what is in that "etc". If all 13 required elements are present, then you could probably use that fertilizer. However, if it isn't made for hydroponics, it probably won't have them, since in soil growing you get trace elements from the soil.

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There is a big difference in general purpose NPK fertilizer and the one specially designed for Hydroponics. The N(Nitrogen) in NPK fertilizer mostly comes from Urea or Ammoniacal form. It is designed to decompose with time and release nitrite which is later converted to nitrate by bacteria. Thus it is more suitable for use in soil.

Plants readily absorb Nitrogen in Nitrate form and hence Hydroponic formula use Calcium Nitrate or Potassium Nitrate as a source of Nitrogen. The point here is, Hydroponics system requires Nitrogen to be in Nitrate form and hence require different type of fertilizer.

What you can do is, use MasterBlend (4:18:38) as your NPK fertilizer and equal weight of Calcium Nitrate and Half of that Magnesium Sulfate as a simplest formula. Note here that this relies on Calcium Nitrate for supplying Nitrogen. For Trace elements, you can use one of the ready mix available in the market.

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