While summer technically ended about a week ago, the hot humid weather and insects clearly haven't got the message so, while we wait for autumn to really arrive, I decided to conduct a continuous flow experiment using my grow beds.

Continuous flow media-based systems usually comprise a watering grid which delivers nutrient rich water from the fish tank to the root zone of the plants.  The water percolates down through the media before draining back into the fish tank.  This regime can be very effective.

The recent 2009 Aquaponics Course Seminar included a field trip that featured a small continuous flow set up.  This system was different inasmuch as it was a combination of deep water cycle grow tanks and media-based grow beds.  The beds were filled with expanded clay media.  The water level was maintained at about 50mm below the surface of the media.

The fish plants in the system were obviously healthy and the water in the fish tank was crystal clear.

While our 4 tank system is excellent for Jade perch, water quality appears to be an issue for our Murray cod and Barramundi.....particularly at the feeding rates that I'd like to achieve.   Our use of auto-syphons (and the way that they stir the water up) is exacerbating our water quality problem.

Replicating the continuous flow (continuously flooded) arrangement was as simple as removing the auto-syphon cores from my seven grow beds.

The beds have flooded up and remain full...overflowing down the standpipe.  Rather cascading back into the tank at periodic intervals (as is the case with auto-syphons), the water now drains back into the fish tank continuously.

The media in this continuous flow arrangement is going to require cleaning periodically but our use of expanded clay will make that an easy task. 

The desired outcomes for this experiment include:

• more effective solids settling
• denitrification - producing mineralisation of settled solids
• effective nitrification
• good plant growth

Some of the prospective issues include:

• nitrification - I normally prefer the percolating action of trickling or flood and drain bio-filters.
• aeration - I've got good diffusers in each of the fish tanks.
• solids build up - will need to be removed eventually.

We may have up to a month to go before we begin to experience optimum plant growing conditions in our our region.  Hopefully, that will be sufficient time to give us some insight into the effectiveness of this type of continuous flow arrangement.