Sunday, February 6, 2011

Floating Raft System

I've finally added floating rafts to my aquaponics system - pics and video below.

The basic setup consists of three 525-liter capacity beds, each with a fitted styrofoam sheet on top with holes for 18 plants on each raft:

Water is continually pumped from the Sump (CHOP Mark II setup) to the fish tank, the two large gravel grow beds and to the floating raft system. The fish tank is fitted with an overflow pipe that continuously sends water through to to a Swirl Filter, and from there to the Sump.

Water pumped from the Sump to the raft system travels through a Matala pond filter to remove suspended solids prior to entering the raft system. Water exiting the raft system and the gravel grow beds, returns to the sump.

If video does not appear above, paste this address into your address bar:

Although gravel grow bed systems do not need particle filtration (they are the filter), raft systems do. This is because in raft-ponics, plant roots are submerged in water 100% of the time, making them perfect landing places for suspended solids, which fish produce large quantities of. Without proper filtration, suspended solids will cover and eventually suffocate the plants.

The Swirl filter in place between the fish tank and the sump will do a good job of settling out heavy solids. By heavy, that means anything that will sink - i.e., not neutrally buoyant. Neutrally buoyant particles (suspended solids), need to be filtered out another way

The particulate filter comes straight from Matala, which builds these for pond filters. It is of course possible to build your own, but the filter sheets come in very large and inconvenient sizes, and I would never have any need for all that filter material. The cost of this purpose-built box with the filters was cheaper than building one on my own, at least with a Matala-type filter. The possible downside is these are designed for ponds of at least 10,000 gallons, so my system is waaaaay over designed in this area. I only want to keep adding onto the system, so I do not see this as a waste, and the shear convenience of getting something ready made and practically "plug and play" was totally worth it in this case.

I started the first two rafts off with lettuce, brocoli, and spinach. The letts and brocs came out of the germination tray they had sprouted in about 3 weeks ago, so I am skeptical they will do that well. I have some new plants getting to planting stage soon that I will transplant in the next few days into the remaining raft and possibly into the others if the plants in those don't look like they're improving.

Raft-ponics is supposed to be the best method for growing lettuce, so I am very much looking forward to seeing how this all works.

My system right now contains quite a large water volume compared to the amount of fish. My tank, which will be able to hold 130-160 fish, is 1,700 liters (450 gallons). The total system volume is about 4,500 liters (1,200 gallons), when you add in the new floating raft beds. This should add a great deal to system stability in all things pH, temperature, and chemical balance, but my guess is that the water has to be pumped through the cycle quite a few times to get the same amount of plant nutrient to the plants. That shouldn't be a problem once my fish grow and populate the tank, but for now it may lead to some slow (but steady) growth. We'll see.

I will be taking the University of the Virgin Islands International Aquaponics and Aquaculture Course next month and will not be making any more significant changes until after completing the course.


  1. That set up must have cost a small fortune.

  2. I guess it's all relative. Compared to off-the-shelf systems and a lot of hydroponic systems, I'd say this is on the highly economical side. It's all DIY except for the pond filter, which I could not have built myself for less than what it cost me retail. The beds are polyethylene - much cheaper than fiberglass, and still food-grade and tough. Styrofoam is cheap. After that, you're talking an air pump andna water pump. Yes, those can be expensive - especially the cheap ones if you know what I mean.