steve wrote:Would the porch support the weight of tank? Water weighs 8.3lb per gallon, so 100 gallons of water would weigh over 830 lbs.
Another question, what kind of tank? Are we talking a pond or glass? Glass is heavy too and risky to use outdoors. A screen should have a grid of 1/2" to allow sufficient passage of UVB. As for the algae... you'll need to explore the different solutions to control it.
there is no way 1 gallon of water weighs 8.3lbs, there is just no way. Think about it...a one gallon milk jug doesnt weigh 8.3 pounds. water at most it is prolly like 5 pounds a gallon.

