A Community and Forum For Aquaponic Gardeners
The Multiple Functions of a Flood and Drain media bed
Flood and drain gravel beds serve multiple functions in a backyard aquaponics system.
1-They contain the bio-filter, they provide the surface area for the bacteria to colonize and they keep the space for that bacteria dark so they function better.
2-They provide the Solids filtration. Contrary to popular belief, in a properly sized system, gravel filled grow beds do not need to be emptied and cleaned. Clogging only happens if the grow bed is overloaded (a 10 gallon grow bed getting all the solids from a 100 gallon fish tank is gonna be overloaded-not properly sized-and will clog.)
3-The gravel filled grow beds support the plants. They can grow most any type of plants.
4-Gravel filled beds provide a place for solids break down, this can also have the benefit of inhibiting future algae blooms since algae breaking down in a grow bed can give off chemicals that inhibit future algae.
5-Gravel filled grow beds are great worm bins.
6-Flood and drain gravel beds provide all the oxygen needed for the bacteria and plants growing in them so no supplemental aeration is needed for those parts of the system (aeration for the fish tank is still recommended.)
In general, Flood and drain media systems require less daily cleaning/maintenance than NFT or raft systems that require solids removal and there is more ease of flexibility in plant growth.
Media systems get a bit heavy and cost prohibitive as the size gets larger and Rafts do make sense for large commercial scale monoculture production.
Drawbacks to media systems
1-heavy and harder to move
2-the heat exchange capacity of flood and drain media can be a negative during some times of the year.
I would venture to say that hobby scale systems that might need to be left to the care of a neighbor over a holiday, are probably safer as media based systems.
If the system in question is going to have fish tanks of more than 1500 gallons and will always have a knowledgeable person to tend it each and every day, then rafts are probably more appropriate
For those systems between 1000 and 1500 gallons of fish tank, and still hobby scale, perhaps a combination system is appropriate and if set up properly, it might not need the daily cleaning.
My system is a combination. All water is filtered by media based flood and drain grow beds and then I have rafts and NFT pipes to use up additional nutrients when needed.
1-They contain the bio-filter, they provide the surface area for the bacteria to colonize and they keep the space for that bacteria dark so they function better.
2-They provide the Solids filtration. Contrary to popular belief, in a properly sized system, gravel filled grow beds do not need to be emptied and cleaned. Clogging only happens if the grow bed is overloaded (a 10 gallon grow bed getting all the solids from a 100 gallon fish tank is gonna be overloaded-not properly sized-and will clog.)
3-The gravel filled grow beds support the plants. They can grow most any type of plants.
4-Gravel filled beds provide a place for solids break down, this can also have the benefit of inhibiting future algae blooms since algae breaking down in a grow bed can give off chemicals that inhibit future algae.
5-Gravel filled grow beds are great worm bins.
6-Flood and drain gravel beds provide all the oxygen needed for the bacteria and plants growing in them so no supplemental aeration is needed for those parts of the system (aeration for the fish tank is still recommended.)
In general, Flood and drain media systems require less daily cleaning/maintenance than NFT or raft systems that require solids removal and there is more ease of flexibility in plant growth.
Media systems get a bit heavy and cost prohibitive as the size gets larger and Rafts do make sense for large commercial scale monoculture production.
Drawbacks to media systems
1-heavy and harder to move
2-the heat exchange capacity of flood and drain media can be a negative during some times of the year.
I would venture to say that hobby scale systems that might need to be left to the care of a neighbor over a holiday, are probably safer as media based systems.
If the system in question is going to have fish tanks of more than 1500 gallons and will always have a knowledgeable person to tend it each and every day, then rafts are probably more appropriate
For those systems between 1000 and 1500 gallons of fish tank, and still hobby scale, perhaps a combination system is appropriate and if set up properly, it might not need the daily cleaning.
My system is a combination. All water is filtered by media based flood and drain grow beds and then I have rafts and NFT pipes to use up additional nutrients when needed.
Replies to This Discussion
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Permalink Reply by William Sherman on
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I really like your ideas. My system, described in the Newbee section, falls in line with your thoughts. It should be large enough to produce some veggies for our family, yet small enough to be tended by our Daughter when we are away. Any comment on my system would be appreciated.
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Permalink Reply by TCLynx on
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I personally think that a system between 300 and 600 gallons of fish tank is probably a good size for providing edibles as well as stability and ease of tending by others. An automatic top up valve set below the normal low water level is a handy thing to make sure the fish can't get too low on water. (depending on system design this could be in the main fish tank or in the sump tank.)
The keys are to make sure things are stable before expecting some one else to take care of it and then make them a detailed easy to understand instruction sheet with step by step instructions for the things you expect them to have to do (like feed fish or net out dead ones to put in compost and take note of how many dead.) Also provide a phone number to an emergency contact in case of pump failure or something like that.
We actually had a GFI circuit go bad while we were gone once. Friend who knows about these things was able to come over and find another circuit to plug into but had there not been some one on had to help out with that, it might have been bad.
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You planted another seed with your comments. I currently have the 250 Gal. Fish Tank buried for gravity drain of my plant beds; however, despite washing the pea gravel pretty extensively before starting up the system, I'm still getting discoloration in the discharge line. You comments made me rethink my plan and I believe I will convert the buried tank into a settlement sump and purchase another 250 Gal. tank to set on top the ground for the actual Fish Tank. I'll use my 1st pump to pump from the sump (settlement) tank to the new Fish Tank. By positioning the pump in the sump at a couple of feet off the bottom, I should be able get my my system cleared up to see my fish again. I also like your idea of the automatic fill valve.
Once again thanks for your views and advice.
TCLynx said:I personally think that a system between 300 and 600 gallons of fish tank is probably a good size for providing edibles as well as stability and ease of tending by others. An automatic top up valve set below the normal low water level is a handy thing to make sure the fish can't get too low on water. (depending on system design this could be in the main fish tank or in the sump tank.)
The keys are to make sure things are stable before expecting some one else to take care of it and then make them a detailed easy to understand instruction sheet with step by step instructions for the things you expect them to have to do (like feed fish or net out dead ones to put in compost and take note of how many dead.) Also provide a phone number to an emergency contact in case of pump failure or something like that.
We actually had a GFI circuit go bad while we were gone once. Friend who knows about these things was able to come over and find another circuit to plug into but had there not been some one on had to help out with that, it might have been bad.
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Even with washed gravel, water usually winds up cloudy for a while. As the system cycles and bio-slime builds up the system will clear. In the future disturbance or new bed additions will clear quicker with an already cycled system. You can also put an old sock or nappy over the discharge pipes to collect some of the dust but these need to be changed often till things clear. Once a system matures the water tends to be more with a slight yellow or tea tint (depending on the media and fish feed.)
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