Hydroponics with Fish and Aquaponics. What’s the Difference?

Both hydroponics and aquaponics grow plants in water. The difference is the source of nutrients.

Hydroponics System

Hydroponics Uses Chemical Nutrients

Hydroponics nutrients are salt-based compounds and growers often talk in terms of electrical conductivity or EC. As plants take up nutrients, the EC of the water decreases. After a couple of months, the water is discarded along with the residual nutrients the plants didn’t take up. Then a fresh batch of nutrients must be mixed with new water and the cycle begins again. This cycle of replacing old water with new water can happen as often as every 2 to 3 weeks. (1)

Hydroponics is as easy of pouring nutrients from a bottle.

But plant growth in hydroponics suffers both when nutrient levels are too high and when nutrient levels are too low. Because the nutrient level declines steadily over the period of a couple of months, there is only a brief period of time when nutrient levels are “just right.”


Aquaponics Uses Nutrients From Fish Waste

In aquaponics, the nutrients become available to the plants through a natural process that occurs in soil-based organic agriculture. Because nutrients are continuously made available in aquaponics, the plants are able to thrive continuously. Because the natural processes involve fish and beneficial bacteria, aquaponics produce will not thrive if the grower uses pesticides or antibiotics. In straight aquaponics, there is never a need to discard the water due to the symbiotic relationship between the plants and the fish. (2)

Aquaponics involves the extra steps of caring for fish, filtering out waste, and possibly using mineralization to extract the extra nutrients in the filtered waste. Because fish feed does not include all of the iron, calcium, and potassium needed by plants, aquaponics growers must add these nutrients to supplement fish feed.

On the positive side, plant growth in a mature aquaponics system will almost always outperform an equivalent hydroponics system. Plants are usually more productive and of higher quality in aquaponics systems. (3)


Combining Hydroponics and Aquaponics

Some growers have fish in their system, but add hydroponics nutrients to ensure their plants are getting a sufficient amount of all necessary nutrients.

The fish in the system demonstrate that the grower isn’t using pesticides. When the majority of nutrients are coming from fish waste, there is a level of assurance that the grower isn’t using antibiotics.

Over time, the salts from the hydroponic nutrients will accumulate. It is like any variety pack you might buy, Skittles for example. If you put a bowl of Skittles out for a party, by the end of the night most likely one or 2 colors will be predominantly left over. Similarly plants in a hydroponics system will selectively choose the nutrients that they want and leave the rest. Leaving an overabundance of certain nutrients in the hydroponics system This requires the grower to change out water as it becomes loaded with nutrients their plants haven’t used.


Some feel adding hydroponic nutrients to an aquaponics system is cheating. But it can be useful to strike a balance between straight aquaponics and straight hydroponics. Learn more about aquaponics and nutrients.



  1. https://thehydroponicsplanet.com/how-often-do-you-change-water-for-hydroponics/
  2. https://www.nasa.gov/audience/foreducators/9-12/features/aquaponics.html
  3. https://www.producer.com/2016/12/go-fish-2/


Written by Meg Stout on April 22nd, 2019.

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