Hi Steve,
The floating rafts have been very successful for the UVI institute and their system is highly productive.
Personally for myself and the concept of backyard aquaponics I like to try and keep things as simple as possible. Floating raft requires the seperate clarifiers, settling tanks, biofilter, etc. Some means of removing all solids from the water before passing it into the areas where your floating rafts are.
Without filtration suspended sediment gets caught on the roots of the plant, building up, smothering the roots, and slowing or possibly killing the plant. Whichever form of solids removal that you use, the equipment will generally require back flushing to remove the solids from the system and this uses up water as well as removing valuable nutrients from the system.
Where as the gravel grow beds, although they are a bit of a pain because they're heavy, there is no wasted water from regular solids removals and all solids stay in the system, breaking down in the gravel grow beds and adding to the nutrients available for the plants. Generally just a more simple method that makes better use of all available nutrients as far as I'm concerned...... But I could be biased.....
