Well what is your overflow and return pump rated at? thats should give you a good idea. My overflow only can do 1200gph while my return pump does 1500 so I figure I'm at like 1000-1200 gph
. I also have 2 koralia 1400's running in that tank too.
As far as flow, most people say a 10 x turnover rate is sufficient. I am a big fan of water circulation though. lol so I tend to go on the heavy side. hehe
You want enough flow so that there are NO dead spots on your sand and rock. I aim my ph's towards each other on either side, pointed up a bit and towards the glass. That gives me a chaotic flow all over my tank. I use purple up, which is very cloudy to see where my flow is going, neat trick I picked up on the forum.
I only use the purple up when I change ph settings though. You can also try fish flake food, follow it around and make sure it doesnt land on the sand and stay there. ie: dead spot lol
You also want circualtion around your rocks as well so the back ph might be aimed towards the rocks but also towards the front so it can meet the other ph's as far as flow and you get a total mess of water flow. Which is good.