I'd look at preventative measures first. At Sahib's research farm, we insulated the fish tanks and have covers made, and on hand, to cover the tanks when we know it'll get cold.
This past weekend, we were in the low 40's here in central FL at night. The raft systems just had their FT covers on all weekend. The systems that are media bed / tower based, I also set timers, so they only ran during the warmest part of the day.
(low 50's)
When I checked Mon morn, they were all in the 62 - 64 range with 'no heat' added.
The smaller system is around 600 gallon , the larger ones are > 2,500 gallons.
Like you said....this is just for 'mild' winter weather....not like last year when it was below freezing every night for over a week...
"Freedom is never more than one generation away from extinction. We didn't pass it to our children in the bloodstream. It must be fought for, protected, and handed on for them to do the same." - President Ronald Reagan
Too many variables yet. How many degrees you need to heat it up too? My winters are a lot different here in TX than my wife's family in Central NY, and their's are different than my family in the Northwest.....
At first I left this blank...but now I believe: "It's better to keep your mouth closed, and have the world think your a fool, than open it and confirm it."
How would you economically heat 5000 gallons to survive a mild winter? Let's hear it!
In Florida, you will probably only have to heat at night and then, just on the coldest nights. Try submerging a stainless steel tubular manifold in a metal 55 gallon drum filled with water. Recirculate the pond or tank water through it and heat the drum water with natural gas (cheapest) or propane, or any other combustible source at your disposal.
Alternatively, enclose the tank in a hoop style greenhouse. The sun will warm the water during the day and the trapped humidity and thermal mass will diminish cooling at night.
I've used both techniques on two of my systems with good results. Granted, my systems are much smaller than the 5,000 gallons you mention, but it's just a matter of scale. The greenhouse thing would work even better with a larger system. I have a 750 gallon system enclosed in a greenhouse tent and the lowest water temp it has reached even on several nights in the mid to low 30's was 55F.
up here, i haven't seen a mild winter like this one in quite a while, but we still get cold..
the only way in our climate would be to heat the building that the tank is in.. big al (who hasn't been around in quite a while) had a double wall hoop house and burned, i think biodeisel, with pvc manifolds to pipe the hotwater through the ft's.. i think the lowest temps he saw were in the 40's..
in fl? i'd insulate the hell our of everything, gb's, sump, ft and cover the ft with plexi backed with foam with a hatch of some sort.. i'd even think about putting 1/2" foam board over the top of my gb's and cut holes for plants
i think adding air in a system that's "tight" would be imperative and this could also be a way to bring some warmth into the ft if you can put the air pump in a warmer area, or use a small heater in a small enclosed space (with appropriate ventilation) to preheat the air before going into the ft..
Wouldn't the above options keep the tanks in total darkness?
Some fish don't need a light cycle to survive, but mine sure do appreciate it.
At first I left this blank...but now I believe: "It's better to keep your mouth closed, and have the world think your a fool, than open it and confirm it."