More flow and add some sort of filter sheet to your canister to grab particulates. If you could somehow get a filter sock in there, that would work well. Also running some carbon will help polish the water up and kick your skimmer into overdrive.
I'm not sure where you got your info, but UV
sterilizers do not kill algae. And in fact, they only kill exactly what goes through them and only if its for the correct period of time. This means you have to have a huge UV
and a low flow through it to kill off anything. It only will kill free floating parasites and maybe algae spores, but anything it kills in the water is fractional to what is already all over your rock and other surfaces. They can be useful for some things, but do not expect them to be an end all be all.
Minimal turnover rate for a tank IMO
should be 15x for proper filtration. So (DT Volume)x15=(Return Pump from Sump)+(Canister Output)+(Other powerheads/flow)
Don't be afraid of too much flow when used correctly. I have seen tanks with 90x turnover rate.