Soak your Powerheads in Vinegar for 1-2 days and they will be like brand new. You make have to scrub them but it should come off with minimal effort. Vinegar is the king of cleaning saltwater stuff.
As far as flow I thought I had plenty when I got it. I have a 220Gal - 4 - 1400GPH and 2 1250's with a 2400GPH return pump but my return lines only let in like 1200GPH anyway so I ported off it to run my Carbon and GFO Reactors.
I did say if you use Chemi-Clean you need to do the other things to attack the reasons for it like GFO Reactor. Check my post.
If is easy, not the cheapest but man what a piece of mind I gain knowing it is up an running. I actually do not check my Phosphates anymore heehee.