The question is often asked if there is a need to add mineral and nutrient supplements to Aquaponics systems. The answer is yes if you want to have nutrient dense vegetables.
In the very beginning, I advocate the use of a seaweed extract such as Seasol for an initial boost in a new system. It gives the new system something to work on and acts as a tonic for the Aquaponics system aiding in the establishment of the beneficial bacteria. It is a very gentle and safe way to get your Aquaponics system started.
A new Aquaponics system needs time to develop all the bacteria and microbes that will convert and release the necessary nutrients for good plant growth.
Aquaponics systems closely mimic nature in the way they handle and provide nutrients for the plants. Eventually there is a myriad of bacteria and other microbes that do their job, just as they should in a mature Aquaponics system.
The job of the two main beneficial bacteria in converting the ammonia produced by the fish to nitrates is very obvious. They are established in a new Aquaponics system usually within a few weeks. It takes time for all the other natural processes to develop and establish.
This is the amazing thing about Aquaponics . The way it becomes so balanced and complete. Never forget, the beauty of Aquaponics is that it is an ECO system. Aquaponics utilises natural processes. The beneficial bacteria, fungal hyphae, protozoa, and nematodes will take up residence in the gravel media beds and do their job of creating nutrients and having them distributed around the system by the moving water
I also advocate the use of "worm extract" or "worm juice or tea" as it is sometimes known. This is done to help “kick start’ the mineral and trace element build up in your new system. Worm tea is not always available to you so the Seaweed extract is a good thing to use in getting your new Aquaponics system up and running.
It should be applied at the rate of a CAP full a day. This can be continued right up to and past when you add the new fish to your Aquaponics system. Seasol will not harm the fish. We have tested and used Seasol for more than six years in our Aquaponics systems and are very satisfied with the results. Natural organic mineral supplements like Seasol work slowly and are not like chemically derived fertilisers.
Seasol or Maxicrop in the USA if you cannot source my favorite product Seasol. Seasol can be applied once every month or two to a mature system and as above for a new system. This will assist in a balanced mineral load and as a tonic for the Aquaponics system. It is a good idea to add it at the grow bed water entry point and allow it to peculate down through the grow media and make it's way around the system carried by the water.
You may find it a good idea to add a half a teaspoon of Chelated Iron to one of the grow beds once a month. Iron deficiency is often encountered in new systems. This is most often a symptom of “Nutrient Lock Out” caused by pH above 7. As pH stays above 7 nutrients are locked up and are not available to the plants even though they may actually be in the system.
Aquaponics systems run best at pH 6.2 to 7.0.
If adding Iron, just use a little water to wash the Iron down in amongst the grow bed media. The Chelated iron can also be added straight down into the water beside the auto siphon device.
This way the iron will be dispersed more slowly around the bed/s. Even though it is added to just one bed, it will find its way around through the entire system.
Potassium and Calcium are also needed in Aquaponics systems. If feeding your fish on commercially available pellets these two elements are often in short supply in your aquaponics system. Once again, potassium is present in Seasol.
Another way to boost trace elements and particularly potassium and iron is to add some raw molasses to the system water. Two tablespoons per 1000 ltr (250 gal) It will turn the water a little dark in colour but will clear after a few days. Molasses is also a sugar so the beneficial bacteria will also get a boost because of the addition of molasses to your Aquaponics system. It is perfectly safe for your fish
These two elements are easily supplied as part of pH control / adjustment.
Murray Hallam's Practical Aquaponics.