Wednesday, August 31, 2011

Media Bed Vs Raft Bed

     The first thing you have to do when getting into aquaponics is to decide which type of system is right for you.  It can seem like a tough decision, and most people you could ask have a favorite for one reason or another.  It's important to pick a system design that'll work best for you.  In this article I'm going to discuss media bed systems and raft bed systems.  Most home growers pick one of these two designs, so we'll focus on them.
Raft Bed system
     I prefer raft bed systems.  Remember that this is just my preference, but I'll try and give a good argument for them.  Raft beds utilize a bed, usually one foot deep, with a raft floating on the water for plants to grow in.  Net pots, rockwool, or another substrate is planted in and then placed in holes in the raft.  The ratio of fish tank to raft bed volume is 1:1 or 1:2.  The great thing about raft beds is that the stocking density of fish in the system is determined by the total water volume in the system.  In example, a 100 gallon fish tank in a raft bed system can be stocked with more fish than a 100 gallon fish tank in a media bed because of the extra water volume from the raft beds.  This is important to keep in mind if you want to harvest fish for their protein.  Another benefit of extra water volume is that there is more of a buffer when it comes to water quality.  Swings in pH and temperature are less likely.  There are more components in the raft bed design, which leads to a higher initial investment.  These designs utilize a mineralization/clarification tank to collect and filter out solids.  This will keep the solid waste from your fish tank out of your raft beds, where it can coat plant roots and hinder nutrient uptake.  But the maintenance on these systems is very simple.  You feed your fish, flush solids about once a week, make sure the water is flowing properly, and add amendments once a week.  It's not hard to maintain a raft bed system.
Media Bed system
      Media bed systems typically have a more simple design, which means it costs less to start up a system.  This can be a huge factor for some.  The downside is that all the solid waste from the fish ends up in the media bed, which acts as your filter.  Media beds function more efficiently when fish are stocked at a lower density because there are fewer solids this way.  If your main concern in aquaponics is plant production this is less of a concern.  And, in my experience, media beds benefit from having a mineralization tank in the system.  One of the advantages of media beds is that planting in a media bed is more familiar to people than planting in a raft.  It also provides more support for the plants if the area the system is in gets a lot of wind.  The media bed is usually about waist high, too.  This is a great feature for anyone who wants to garden without all the kneeling and bending over.  There is less maintenance in a properly designed and stocked (fish) media system.  The media bed acting as a filter cuts back on the need to remove solids manually.
     Either of these two systems are a great choice.  Like I said, it just depends on you and what you want.  I hope this helps you make a more informed decision on which system is right for you.  If you need any more information or advice shoot me an email and I'll get back to you as soon as I can.

Brendon Tripp
Trinity Aquaponics

1 comment:

  1. It is a good idea to have a mineralization tank, even in the media bed type. The cost of having even two mineralization tanks is very low and that improves on the bacteria reproduction, prior to feeding the water with nutrients to the plants. So, I think a CHOP (Constant height one pump) combined with one or two mineralization tanks is a good idea.