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After 'mastering' the build and balance of the ebb and flow system, I wanted a new challenge.. a floating raft system similar to Dr. Rackocy's (i've read all of his papers and I'm a fan).


My friend Pat, who is interested in aquaponics, has plenty of space in the basement of the house he is currently renting.  So, I came up with a build that will fit into a designated area in his basement, and is manageable with materials that we can obtain.


Below I have posted the build plan, some of the reasoning behind it, and the cost of materials. I estimate that this project will cost ~$1,000.  I havent calculated the yield yet, but when I do, I will post it here.  I will also post the project progress pictures.

The plans below are fairly well scaled, I am not 100% on the watts per sq ft for the grow lights.  I know my pump may seem a bit high, but it's my preference to have a higher gph rate.  Circulating the water 3x and hour is a minumum for keeping healthy fish.


Floating Raft System

Grow Bed:
Container Dimentions: 10 Ft x 4ft x 16 in (1.3334 ft) (LxWxH) = 53.336 ft^3 = 398.98 gallons
Water Dimentions: 10 Ft x 4 ft x 14 in (LxWxH)  = 46.6667 ft^3 = 349 gallons  
349 gallons x 8.35 lb/gallon = 2914 lbs (over 1 metric ton)
Cinder block base, Thick plywood bottom and sides, supporting structure is 1x2 boxes around the plywood.  Since the floor is not 100% level and neither are the cinder blocks, some sort of thin rubber sheet should be stacked until the bed is 100% level.  (349 gallons of water weighs a lot, you want uniform distribution of the weight)
Plywood must be briefly sanded and then sealed with 2 coats of polyurethane (to protect from water damage/degradation)  
Inner lining must be with 6 mil (or preferably thicker) plastic sheeting (LDPE - because it is food grade). Sheeting must be double lined and stapled to the outer/upper rim of the wooden tank.  Make sure corners are folded appropriately so that there is minimal access into the folds. (the plastic sheeting must be folded at the corners since it doesn’t come in a box shape.)
Floating Raft:
2” Dow Corning blue board is recommended by Friendly Aquaponics
Wood Supplies:
All plywood comes in 4 ft x 8 ft (or 2 ft x 4 ft) sections  a minumum of ¼ in thickness should be used.
Home Depot - 15/32 thickness plywood (solid pine) is ~$27 per sheet (4x8ft)
*could possibly use particle board, ½ in thickness at least
-2inx4inx10(10 feet) $4.78 (pine)

Will need at least six 4ft x 8ft plywood pieces and eight 2inx4inx10ft pieces
1x  10 ft x 4 ft plywood
2x 10 ft x 16 in plywood
2x  4 ft x 16 in plywood
4x  10+ ft in 2x4’s
4x 4+ ft in 2x4’s
Wood/Deck Screws >1.5 inch ($10-$20 depending on the size of the box)
Corner brackets x ~16 ($2-3 each)
1 Gallon Polyurethane $37
Brushes ~$5
6+ mil LDPE or better, 10 ft x 15 ft x 2 needed to cover bed (50 ft x 10 feet $31)
Staples for staplegun $4

Fish Rearing Tank(s):
2 x 55 gallon drum (water volume will be less in drum, ~ 45 gallons/drum) more than 2 drums can be used, a passive overflow/cascade system will be used.  Water will be pumped into the first drum. When the water level is high enough it will overflow into the second drum, etc...  the drums should be set up on raised platforms where the proceeding drum is a specific height lower than the preceding one.  this is to maintain the same water level height/volume in each drum.
Bulkhead fittings will be used to seal the holes drilled into the side of each drum for the overflow pvc pipes.
Bubblers must be installed into each rearing tank to promote circulation within each tank and oxygenation of the water for the fish.

2 or more 55 Gallon drums.  (normally come with sealed top so part will have to be cut out.)
-$67 each from uline
Bulkhead fittings (1.5 to 2 inch) (double slip) $8 on amazon
1.5 inch to 2 inch pvc piping ~2 ft worth $3
1.5 to 2 inch 90 deg pvc elbow fittings $2.50 each
gutter screen  $4 (6 in x 20 ft)
standardized thickness material for raised platforms (bricks?) $0.43 each 7.75x2.25x3.75 inch
air pump (multiple outlets) ~$27 with 4 outlets
air tubing and airstones ~$12 for the tubing and ~$4 for the stones
silicone sealant  2.8 oz $5.50

Solid Waste Filter:
Solid waste filter should be placed after the fish rearing tanks to minimize the amount of solid waste that enters the grow bed.  Or a finer filter media will be placed under the inlet from the rearing tank overflowing into the grow bed.  
A smaller volume bucket/drum could be used (15 to 30 gallon) in line with the fish rearing tanks

15 Gallon Drum $41 for 1 from uline
30 gallon $71 for 1

Total system water volume: 349 +45 + 45 = 439 gallons
To circulate the system total water volume a minimum of 3x and hour, a 1300 gph pump will be needed.
I already have a 1300 GPH pond pump (~$120), just need a 1’’ screw in fitting for the 1’’ hose.
1’’ braided PVC hose about $30 worth (20 ft)

-Lighting must cover the grow bed area, an approximate  (6.4?) Watts of white/blue spectrum will be used per sq ft of growing space.
-T8 bulbs will be used
Four 2-bulb (32 watts each) shoplight fixtures will be used to cover the 40 ft^2 grow bed area (thus the 6.4 watts per sq ft.)

Home Depot - Lithonia Lighting 2-Light White T8 Fluorescent Residential Shop Light

Model # 1233 RE
Store SKU # 565027
$12.97 each x 4  = $51.88 *1.08 (tax) = 56.04
Bulbs are ~$8 for a 2 pack

Dual outlet timer ~ $15 x 2 = ~$30
Extension cords ~$10 Each x2 = ~$20

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The UVI setup is a useful design for big systems for say 20000 gallons but doing it for a small 400 gallon system doesn't make a whole lot of sense unless you want to have a high fish density and want to do maintenance every day that this system demands.

You could achieve the same clarity/nutrients in you water (with less fish and thus fish feed) by just running your water through a media filled grow bed before going to your DWC raft - Otherwise known as a hybrid system, which many people are doing now. Why not do this?

You will also need aeration in your raft to keep your plant roots happy.

Lighting - 6.4 watts/sf won't be enough. Using T8s the lights have to be just inches away from the plants so you will need alot more bulbs and fixtures to get good results. There are many treads here arguing Metal Halide & High Pressure Sodium lights are dollar for dollar more effective per watt than florescent lighting. Also the cost of fixtures and components are comparable. I use 150w HPS for 4sf of grow space and my plants do great and I don't have to worry about mercury contamination if a light breaks. If you want flowering & fruiting plants then you don't really have a choice anyway because florescent won't get you there.

Thanks for the review Jon,

I was more inspired by the UVI system, I wont be doing "high" stocking densities.   I do agree with the media bed as a better  filtration/clarity method, but to clean that is more invloved compared to opening up a valve at the bottom of a bucket to remove the sludge, and I am limited in space, so adding another grow bed is at least another 2 sq ft.  That's why I'm gonna stick with the solid waste filter.  I have a 5 gallon bucket as one now and it works good enough.


Aeration in the raft is no problem, I think the air pump i budgeted for had 4 outlet ports.


Lighting, I had a feeling the watts per sq ft was low.  Adding more fixtures is not a problem.  You do have to keep the lights closer to the plants, but this system is only going to grow green (non-fruiting) plants.   I have a 150W HPS light as well, but my plants always stretched towards it (unhealthily), rather than filling out.  I wish there was a bulb that could balance that out.


Correct me if im wrong, but the HPS bulbs emit light around the red spectrum, which is why they are more for flowering/fruiting plants.   Also, growing fruiting plants in a raft system, while possible, is harder because of the size and weight fruiting plants have, compared to lettuce or herbs.


Im doing this more as a new challenge, and as a showcase for urban growing.

I have done course work at Nelson & Pade and with Dr Rakocy so I understand the appeal of his system. I disagree with you about how much space UVI filtration method will take up as opposed to a grow bed. The UVI method done correctly requires 4 stages each with their own tank respectively. 1) Clarifier or Swirl filter 2) Bird Netting 3) Matala Filter 4) De-gassing. All of this takes up space ...  instead have a grow bed to perform all those functions and grow food to boot. A properly designed grow bed that is not overloaded with waste, combined with red worms should never or rarely need cleaning.

But hey, as an experiment and homage to Dr Rakocy I can understand the mad scientist in you.

My leafy greens do great with the HPS. I keep the light about 12-18" above the vegetation.

alright i havent tried the worms yet, that something new to look into.  I wasnt trying to mimic his system exactly with all the filtration steps.  just doing what i can within my means.  the swirl filter is a pretty passive filtration step, that's why i like it.

would you recommend using lava rock for the majority of the filtering grow bed? i like using it because of the high surface area for the bacteria.

when i used the HPS light, it was my cayenne pepper plants that really stretched toward the light, stretched so much that they would eventually fall over, so i would prune them back.

Nothing is more passive than a media filled grow bed, but all that filtration is cool and fun. However, If you don't do those additional steps over time the fine solids will settle elsewhere including on the roots of you plants. You can have brown roots which don't get O2 and anaerobic zones where the fine solids build up. This can cause ammonia and nitrite spikes and kill fish. That is why those steps are used, from years of experience of trial and error Rakocy made those mistakes.

Sean I don't want to steer you in a particular direction, I'm just sharing what I have learned being a student of the masters. I qualify my real life experience with DWC as zero... yet I have designed my own system based on the work of Rakocy also with some input from Dr. Wilson Leonard and awaiting a building permit for my greenhouse.

As to lava rock I have no experience, people do use it but often at the bottom of the bed because it is so hard on hands. Fill up the top with expanded shale or expanded clay.

I also found that as my grow bed matured that the plants stretched much less for light. The latest pepper I grew in it was a monster.

Well, you've got me thinking now.

The grow bed before the DWC tank, is it an ebb and flow system?  I am trying to get away from that due to the fluctuations in the tank water levels. 

If it was a ebb and flow system, it would be very fast due to the high flow of water (1300 gph).  Which is not a problem for the plants, but for the red worms?  I havent looked into them yet, but i will.


I have used freshwater shrimp to keep my aquarium tank and it's aquatic plants clean, do you think they would help in this scenario as well?

The flow would go something like like this :

=> Highest Point: Fish tank ==\/

||                                      Media Bed =bell/loop/u siphon==\/

||                                                                     DWC ===>  Sump === (pump)==\/


So yes the Media is Ebb and flow. You add water/iron/buffering to your sump. The parts of the system that the water changes levels is of course the media bed but also the DWC as the grow bed drains and the pump pumps water to the fish tank. There is so much water volume in the DWC that level changes will hardly be noticed... the fish tank is always full. I think that if you size the media to be the same size or a little larger than your tank you can reduce the size of your pump to replace fish tank volume 1-2x per hour. Given that your growbed of the same size will need 1/3 the water to cycle you should have your growbed flushing 3-5 times an hour.

Worms do fine in water, they breath through their skin and can even live at the bottom of a tank or water if the water is well aerated. You may find that they move around your system like flow out of the siphon into the DWC if you don't have safeguards like screens for filters. You still may want to have a matala filter between the siphon and the DWC, worms will probably live in there too.

A lot of people are doing freshwater prawns in their DWC, they probably won't hurt

Sean said:

Well, you've got me thinking now.

The grow bed before the DWC tank, is it an ebb and flow system?  I am trying to get away from that due to the fluctuations in the tank water levels. 

If it was a ebb and flow system, it would be very fast due to the high flow of water (1300 gph).  Which is not a problem for the plants, but for the red worms?  I havent looked into them yet, but i will.


I have used freshwater shrimp to keep my aquarium tank and it's aquatic plants clean, do you think they would help in this scenario as well?

I use red lava rock in my ebb and flow system. Yes, it is hard on the hands and it can be difficult to get the rocks out of the roots when pulling a plant. I had initially planned on using perlite, but this just floated away. So I did half perlite and topped with lava rock to weigh it down. Now, I occasionally get pieces of perlite clogging my pump. I wish I had gone with expanded clay from the start, seems worth the money looking back.

However, if you decide to go with red lava rock I have one important piece of advice: WASH THE ROCKS! Red lava rock has a lot of dust that will cloud your system. Every time I add water to my sumps I stir up silt. I think the only why I could ever get rid of the silt would be to completely change out my water, wash the rocks, and start over.

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