Welcome to Pond Boss!

I'm not sure of the answers to your question, but I do know that pumping water uphill takes a lot of energy.

The algae issues could be from several factors including nutrient load in the water, as well as maybe stagnation.

If the ponds go dry in the winter, or freeze solid, then stocking of fish may be a futile effort, unless you're willing to restock each year.

Excerpt from Robert Crais' "The Monkey's Raincoat:"
"She took another microscopic bite of her sandwich, then pushed it away. Maybe she absorbed nutrients from her surroundings."