That expression of what goes around, comes around can equally be applied to aquaponics and the biofiltration mechanism that keeps the whole system flourishing along nicely – the growbeds.
The filter system where the billions of bacteria survive can eventually get clogged up with fish solids and “dead zones” appear that turn the system nasty and unfriendly to growing plants or fish.
The question was how long will it take for the fish solid waste – the fish poo, to build up to the point where some maintenance was needed and the system filter material the clay beads or hydroton or stone gravel media would eventually need to be taken out, replaced or cleaned?
It was generally thought that the amount of fish solids and waste build up without any supplementary solids filtration would take around 18 months depending on fish load and growbed size and so on.
But with the introduction of compost worms that period for many aquaponics enthusiasts seemed to extend the life of the system and go on from one year to the next.
Worms are efficient to a certain extent but they are not the entire solution. The eventual question amongst members was how long before the system would crash and fail?
Every year was another milestone for us at Practical Aquaponics. We build some of the best Grow Beds in Australia from durable 300mm deep fiberglass.
Our troughs are large solid and deep construction and seemed to go on from one year to another without maintenance.
Many people felt that aquaponics system once running correctly were bullet proof and no maintenance was needed. But this is not true as I am the first to admit.
Maintenance is required right through a well run an aquaponics system, For example, we had a client return a pump that had clearly been run “dry” and was badly damaged. Became agitated when it was suggested that the pump had been run dry. “How can it be run dry when it is submersed in the fish tank????” he shouted with colourful adjectives.
Easy really, the pump filter screen had never been cleaned, therefore the underwater pump was getting next to no water flow and in effect running dry. Terminal damage to the pump was only a matter of time. Same principle applies to the growbed.
Anaerobic Dead Zones
This is what happened in our five year old growbed system.
This particular system has, over the last few months started to show a slight rise in pH instead of the typical slow drop, which is a pretty good indicator of anaerobic areas in the system somewhere. I suspect one or two “dead” areas in this bed.
The solution was to dig out the media and wash it. I decided to replace the entire gravel media and use this old media to fill in pot holes in his driveway! Nutrient rich potholes! It was very obvious that this bed was the one having difficulties. Over the life of the bed I had added a good amount of granulated mineral rock and this had broken down and had become "soil like" which would be good in a regular garden, but in here it was inhibiting the grow bed in its role as a bio filter for the Aquaponics system.
Two of the other beds are doing just fine. A third bed that has also had numerous toppings of mineral rock fertaliser is approaching a maintenence session.
Three quarter inch gravel was used to replace the media in this old bed. The new gravel was shoveled in and leveled, then the water turned back on to start the fill and drain cycle via the auto siphon..
Altogether about two hours work for myself and Lee to replace the gravel. This new bed will take a number of weeks for the bacteria to reestablish and begin another 5 years of productive service producing an endless supply of vegetables and fish. The nutrients that are travelling around in the water from the rest of this mature system will immediately provide for the needs of the new seedlings. This four bed Homestead Aquaponics system has a brand new grow bed / bio filter. It will be interesting to observe the pH over the next few weeks to see if it begins to gradually drop, as it should.
Nothing is “self sustaining” or maintenance free in this world. Everything requires some work and if I really have to dig up a (grow) bed once every 5 years, I reckon that is darn good. What other gardening method can give 5 years clear service of just planting and harvesting?
If you want to learn more, get my Aquaponics Secrets DVD which takes you into the fascinating world of bacteria, growbeds and fish health in more detail.
Our DVD's are produced by ECO Films