Since we had a pool, i had other things i used and one was a solar bubble cover. I cut them to fit over the water. I didnt put the tops on the barrels because it would make it hard to keep them full since they hold up my tables. So far, we've had no problems with mosquitoes. By fall, the water had dropped down to about 1/3rd down. I refilled them, cut new covers and all is good. I had planned on emptying them during the summer because i really thought they would be a mosquito problem, but it got to hot to even go in there so the water stayed. There was a bit of algae clumps but nothing smelly or gross. Its still in the experimental stage as far as how i keep water in them, but they were a success at holding heat and keeping the greenhouse warm on cold nights. Last year the only time i had to use heat was when we got covered in a foot of snow and had no sun for days. I'm guessing that as long as we dont have that again this year i will not have to get out my heaters at all. The room is 12x16, covered in double walled polycarbonite on 3 sides and roof, north side is still metal which isnt insulated yet and i suspect that i'll hold in more heat once that wall has insulation. The floor is reclaimed rock from a creek bed where water washed rock off the road. My main plan with the greenhouse was to house my hanging baskets over the winter. But i now have so much fun starting seeds and growing things, i need a bigger greenhouse now.
