Nutritional requirements of the fish for those minerals (iron, calcium, potassium, magnesium, etc.) are far less compared to what the plants actually need.

Aquaponics is the combination of aquaculture and hydroponics into a recirculating system where the plants utilize the nutrients derived from fish production and — in return — the plants, by absorbing those nutrients, clear the water for its eventual return to the fish tanks. The entire cycle is repeated.

Unfortunately, there is a problem regarding nutrient deficiencies for the plant production side of the equation. Note that the nutrients that the plants use are from fish production. Consequently, this means that it came from the fish feed. Because the fish feed is designed for the nutritional requirements of the fish, and not of the plants, there will inevitably be nutritional deficiencies on the part of the latter.

Off hand, at least based on the UVI model, the fish production side can cover around 80 percent of the nutritional requirements of the plants. This can be improved by adding a mineralization tank where the solid fish waste can further be broken down into their mineral components for further absorption of the plants. Nonetheless, working with that 80 percent benchmark, the remaining 20 percent must be provided through supplementation.

What is often lacking — for the greens — are iron, calcium, potassium and magnesium. As a result, there is poor growth, yellowing of leaves, and problems with the fruits (ex. tomatoes suffer from blossom rot). The question thus arises, why not just create a fish feed that can take care of the nutritional requirements of both the fish and the plants?

That’s a good question to ask. But there are realities on the ground (or in the water, so to speak) that make this proposal difficult to implement. For example, the nutritional requirements of the fish for those minerals (iron, calcium, potassium, magnesium, etc.) are far less compared to what the plants actually need. If we bombard the fish feed with supplements, how will that affect the health and growth of both plants and fish?

This is an area that must be studied first before designer feeds for aquaponics become a reality. Otherwise, there will likely be unintended results that may cause more harm than good.

Another issue that arises involves buffering the water to pull the pH back up as the aquaponic system matures. Remember that pH tends to go down as a consequence of the nitrification process.

This requires the addition of “buffers” to pull the pH back up to its ideal range (preferably a pH of around 6.8-7). To accomplish this, calcium hydroxide and/or potassium hydroxide are added to the water.

Now, if the potassium and calcium which the plants require are already in the fish feed, and you still add both — this time to the water — to pull up the pH of the system, then there will be an overabundance of calcium and potassium. This will definitely have an impact on the water quality, the fish, and the plants. Whether it’s good, bad, or (hopefully) negligible is a subject that must be further studied before any conclusions are claimed.

There are still many areas in aquaponics that are being studied. As new discoveries are made (preferably scientific rather than anecdotal), these contribute to existing knowledge about the topic and to the improvement of a technology that can shepherd wasteful food production practices towards sustainability.