Some years ago, I had a fish import business. At one point, I leased some greenhouses, that had been used, previously, for growing potted plants. The houses had concrete benches in them, that were 5 feet wide, and 100+ feet long. They were sloped to the center and, also, to one end to facilitate drainage of excess water from the plants. (See diagram below) When they were growing the plants, sections of half round clay drainage tile were placed down the center, and a layer of gravel was placed on top of them. The pots were on top of the gravel, and the water drained through the gravel to the center of the bench, ran under the tiles, and drained out at one end.
I decided to convert the benches, in one house, into little fish pools. I did this by cutting boards to fit across the bench, about every five feet. Then I fitted more boards between these at the center line of the bench. I painted the boards with plastic, (polyester fiberglass resin) and fastened them to the concrete with strips of resin soaked fiberglass. This resulted in 150+ pools that were 2½ X 5 feet, about 90 gallons. I left a few of them bigger, 5 X 10 feet.
Besides the fish, each week we got shipments of aquatic plants. One of the varieties was corkscrew Valisneria. They came tied in bundles of 100 and, some weeks, we would have a few bundles left over. Rather that throwing them out, I figured I'd try to grow them. In one of the 5 X 10 pools, I spread a 40 lb.bag of dehydrated cow manure, and covered it with 6 cu. ft. of peat moss. On top of that I put down 300 lbs. of #3 aquarium gravel, and planted 300 plants. The plants took up about one third of the area. The water, almost immediately, turned bright green I flooded the pool over the top, a couple of times, to get rid of the green water and, as the plants started growing, and became established, the water gradually cleared. The plants put out lots of runners and, in a short time, formed a dense mat that covered the entire bottom of the pool. I could cut out a 6 inch clump, and that was about 100 plants - never bought corkscrew Val. again!
I threw in 3 pairs of large Blue Gouramis and, within days, had three nests, on different sides of the pool. After a few months, I started pulling out 1 inch BGs and, over the next several months, got 3,000 of them.

Attached Images

greenhousebench.jpg (7.7 KB, 3 views)

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John