When Grow Beds Get Old….What Happens? Maintenance Is What Happens!

When Grow Beds Get Old....What Happens? A five year old gravel grow bed.

Years ago there was an old expression applied to computer industry surrounding software programming – “Garbage in – Garbage out!”
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?

Profile of a five year old gravel grow bed that has reached the end of it's life.

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

Muck and rubbish from the very bottom of the 5 year old grow bed.

Anaerobic bacteria begin to colonise parts of your growbed in areas where oxygen is not being delivered. The good aerobic bacteria are replaced with the other sort. A good tell tale sign is the pH will give you warning signals. Instead of creeping down gradually becoming more acid as it does in a healthy aerobic system, the pH drift will halt and reverse and become more alkaline.

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.

Lee uses a spirit level to screed the new gravel. It is all ready now to plant the seedlings.

Replacing the Gravel
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

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9 Responses to When Grow Beds Get Old….What Happens? Maintenance Is What Happens!

  1. shea says:

    Hello Murry,
    I have a relatively new grow bed and I noticed on one of my Zuchini stalks that there was some fungal type growth. Any ideas on why some fungal growth would occur on plants on the grow bed?


  2. Murray says:

    Fungal growth can occur anywhere anytime, Zucchini, cucumber and the like are very susceptible to fungal attack. Spray with milk or potassium bi carbonate to assist in control. Will not eliminate the fungi but will keep it to a minimum.

  3. trebel says:

    thanks for the explanation, it was very informative, always glad to read your information, great thanks.
    cheers boss.

  4. Sherman says:

    If you put a solids filter on before the growbeds will this extend the life of the growbed before maintenance is needed and if so for how long. Another question I have is, is it necessary for the solids to get to the growbeds to add nutrients or are the nutrients just in the water. Thanks

  5. Murray says:

    Hi Sherman,
    Yes, adding a pre filter to the system will extend the life of the grow bed, but 5 years useful life is pretty good. How much life do you want ???? Adding a pre filter will require additional maintenance, the filter will need cleaning and the resultant solids treated or discarded. For most home systems this is much less convenient that the prospect of a “once every 5 years grow bed overhaul”
    You may have missed it in the article, but 3 of the 4 grow beds in that system are still going strong. It will be interesting to see how long they go before needing attention. As I pointed out, the 5 year old bed just cleaned had been dosed heavily with mineral rock during it’s life. I am certain that this is the main factor in the maintenance requirement for this bed.
    Due to the mineral rock I observed in this bed a much lower worm population than exists in the neighbouring beds. As you would know , worms have that capacity to reduce the volume of organic matter by up to 80%, and while they are doing that they release all the minerals and nutrients that are in the fish solids. The presence of worms in the grow beds is a wonderful thing. Aquaponics is an ECO system.

    As to how long before maintenance is needed???
    Depends on a lot of factors such as how many fish you have in your system, what species of fish and so very importantly, how many plants you have in the system. As you would know, the plants use up the nitrates and other compounds that originate in the fish waste.
    The plants are what separates Aquaponics from Aquaculture. In Aquaculture elaborate filtration is required to collect and remove the fish wastes, then nutrient rich water has to be run-to-waste. In Aquaponics, the plants and the proportion of them makes all the difference to the entire system. The synergy between the plants and the fish is just a wonderful thing to watch and enjoy.

    Are the nutrients just in the water?
    Yes they wre eventually, initally they are in the fish waste. They are converted and released by the action of beneficial bacteria and of course, the worms. They (nutrients) are transported around the system via the water and ultimately used by the plants.

  6. TCLynx says:

    Wow, yea I guess the excess rock dust and fewer worms do make a big difference.
    How long definitely also depends on fish load, rock size, root mass and other things like the flood and drain cycle and type of plants etc.
    I’ve seen a poor tiny 10 gallon grow bed become clogged in a matter of under a year when trying to handle all the flow from over 100 gallons of water with fish and duckweed along with the root mass of MINT. And I’ve had other grow beds that have been running continuously since 2008.
    The type of plants and their root habits play a huge role in how quickly a bed can become clogged. I think certain plants and beds could go along indefinitely with no extra special full bed overhauls while something like a banana which loves to create it’s own hummus by growing lots of fine roots and then letting them die off to grow more will clog a bed in about the time it takes to fruit (in my case about 6 months.) Corn and tomatoes have proved to me they like to send big root masses down the drains and I need to check the stand pipes at least once a month but I suspect come the cool season the worms will do their job of clearing out the excess roots that don’t come out when the plants are pulled.

  7. Murray says:

    Hi Tcylnx, Thanks for your input,
    Yes you are absolutely correct re the roots of various plants. I feel that is why I have had such success with the Pawpaw (papaya) Their root system is very well spaced and allows good worm movement around the grow beds. The beds that the pawpaw are growing in are also 5+ years old and are showing no signs of needing attention.

  8. Andrew says:

    Is there any way to do continuous maintenance on the beds, i.e. remove only a small portion of the media on a regular basis?

  9. Murray says:

    Hi Andrew,
    Really that would be overkill a lot of work for no good reason. I really do not know what I could compare it to….perhaps stopping at every service station (gas station) and putting a small amount of air in my car tires so I don’t have to pump them up in 5 years time.
    If you are really worried about solids build up in the beds then add more beds or a pre filter.

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