I got tired of not seeing my fish for most of the winter months, but I like the warmer temperatures that covering the pond provides, so after many trial versions, I just finished this latest version. It’s not very pretty, but it’s working well.
These pictures are what I had been using...
The cover is made from 1½” PVC arches on 30” centers and covered with 1 or 2 sheets of 6 mil plastic from Home Depot. The pond is about 23ft long and 14ft wide.
To add both pressurized air and heat under the cover, I ran an 8” insulated duct branch off from my main house electric heat pump heating circuit and weighted the edges of the plastic down tightly. This arrangement both provides inexpensive heat and blows off the CO2 that accumulates under the covering. This will not work with gas or oil heat systems as they give off exhaust fumes. The blue weight tubes are 3” flat drainage hose filled with course sand and the ends are rolled and taped shut with electrical tape.
Window frame work
When you cover a pond, you trap Carbon Dioxide (CO2) gases inside. As you know the fish and all the other living things in the pond use Oxygen and give off CO2 even in the cold of winter. So if the CO2 cannot escape, it builds up in the air and in the water. If it builds up enough, it will stop the fish’s gills from releasing the CO2 in the blood and the fish will suffocate and die. Also, excessive CO2 is acidic, so it will push your PH lower and you can get a PH crash which will also kill your fish. So it’s really important to add a source of outside air under the cover. The more air the better, but depending on your pond size, even a few large air stones driven by decent size air pumps will work for most people.
I left the PVC arches in place for this year and just added the window framing over them. The window is a 48” tall x 60” long vinyl sliding window with double pane insulated Argon filled glass from Lowes. This type of window and the heated air, keep the window from frosting up. You could use a smaller window; I went with a taller window to get a steeper angle for the snow to slide off and also so that I don’t have to bend down to look in the pond. It’s important to build a solid frame around the window so that it does not flex and break the Argon seal. Once the window is framed, you can position it anywhere you want to. I used 2'x6's angled down across the pond and 2'x4's on the bottom to secure the window in place.
For the covering, I switched to bubble wrap from www.SolarCovers.com, it's their Crystal Clear Solar Cover and it's available in many large sizes. It is 16 mils thick, so it's almost 3 times thicker, yet it is letting enough sunlight thru that I'm still getting green algae on the pond bottom and walls.