For you who is in Florida, building a 5000 Gallon tank outside not only heating it will be an issue, but also cooling it during summer time, depending on what type of fish you will have in it will be another issue.
Building a fish tank is really not that difficult. In order to control the temperature, building it with wood and insulating it got some advantages. Here is how to build a fish tank using 2 X 6 X 10[attachment=2:1qkm5c0o]FT Build up 1one.jpg[/attachment:1qkm5c0o]
[attachment=1:1qkm5c0o]FT Build up 5.jpg[/attachment:1qkm5c0o]
[attachment=0:1qkm5c0o]FT Build up insulation 3.jpg[/attachment:1qkm5c0o]
For a 5K Gallon fish tank, you may use 2 X 6 X 12 and build it for 6 ft of water depth, so 8 ft hight should do it. By the time you add insulation, and then your EPDM, you will have at least a tank with 11.4 X 11.4 size. If you fil it short of 6 feet. you get more than 5K Gallons..