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Todays project was building the raft tank. I used a 4 x 8 (1200mm x 2400mm) sheet of ½ inch (12mm) plywood and 2 x 12 (50mm x 300mm) pressure treated lumber. I built the box using 3(75mm) long wood screws. I put the plywood on top, and screwed it down around the edges with 2 ½ inch (62mm) . I turned the whole thing over, added some corner braces to give extra support. Then using 2 x 4 (50mm x 100mm) lumber I framed an extension to the box, giving me a total of 15 inches (375mm) that lets me have 12 (300mm) of water and 3 (75mm) of head space for the raft to float in. With the help of a son in law, we moved the whole thing into the greenhouse, set in the base shown in earlier pictures.
For the liner, I used dead vinyl. A neighbor of mine mentioned he knew a billboard sign salesman who could get me old billboard sign vinyl. I told him to keep his eye out for some. The next day he showed up with a folded up bundle. Today we rolled it out and it turned out to be a 14 x 32 McDonald's billboard sign. The outer folds had breaks in the folds and I was afraid it would leak. When we unfolded it, we found that the inner part was still pristine and without breaks. I cut a piece extra big and we hauled it into the greenhouse and laid it in the DWC bed. We positioned it and stuffed it into the corners. Then using a hole saw, I cut the holes through the vinyl and the lumber for a 1 (25mm) bottom drain, and a 2 (50mm) overflow drain on the end.
On bit of advice, DONT try to cut the hole in the vinyl using the hole saw, bad bad idea. It grabs the vinyl and makes a mess. Lift the vinyl up and cut the hole through the wood. Then use scissors to carefully cut a rough hole SMALLER than the hole through the wood. Then twist/force the bulkhead fitting through the vinyl, stretching it and making a nice tight fit.
I attached the two bulkhead fittings and tightened them up. Then we smoothed out the vinyl and started filling the bed with water, smoothing the vinyl and making sure it went in the corners. I capped the bottom drain, and put an elbow on the overflow that dumps the water into the sump tank. It makes a very low cost, effective DWC bed.
I only have 1 question, does the lettuce like French fries?
Pictures below:
1) Corner detail showing the DWC frame.
2) Laying out the vinyl
3) DWC filled and operating (minus the foam).
4) Picture of the end with the overflow you can see the smaller PVC coming out from underneath for the bottom drain, and the water falling from the overflow into the sump.
Yes, another full day spent. Now I need to get a 12VDC backup pump and a 12VDC aeration system hooked up. Another problem I have to solve is the water heater heat control is not sensitive enough; the built in temperature controller in the water heater has to much variation and is going to cause fish stress.
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