I'm installing a 2" flexible line to a small holding pond which will supply a fountain/waterfall. I (think) I need to install 2-90 degree fittings to get my 2"pipe perfectly vertical. What is the best practice for "turning" water 180 degrees with minimal flow rate loss?

Thanks in advance.

obviously, the gentler the bend, the less resistance you will have.
eight 22 1/2 deg bends would be overkill but give you the least resistance.
four 45 deg bends would be the more common sense approach.
after that (if available) long sweep 90's would be better than short sweep 90's

Thanks, packy

Use electrical bends rather than elbows.

Do I lose 50% flow at every hard 90?

Not even close to that much. If that were true a 'labyrinth" might not have any water flowing out of it.

Not to split hairs, but an infinite 50% reduction series would never reach zero flow much as the onld Math query: "If you start at the 50 yard line and each play moves 50% of the way to the goal, how many plays does it take to cross the line?"

That said, what quantitative advantage does a curved 90 have over a hard 90?

Turbulence which is a flow restrictor.