Proper Flow in Tank

Hi All:

I am trying to figure out how much flow to have in my tank.

I have a 92 gallon bow front.
Temp: 79-81
Ammonia: 0
Nitrites: 0
Nitrates: 5-15 depending on the day
pH: 8.2
Sal: 1.0225-1.025 refractometer


Residents:
3 green/blue chromis
2 ocellaris clowns
3 purple eye anthias
1 red flame angel
1 cleaner shrimp

I have about 40lbs of LR. I also have a sandbed about1" to 2" depending.

I have 3 hydor/koralia 750/850 power heads. One on each side at about a 40 degree angle down to the middle. Another in the back pointed toward the surface for agitation (in combo with the two returns up there).

Sometimes the fish seem to like the stream in the middle. Sometimes they do not. Right now I have one on each side (not the one toward the top) off and everybody is out swimming. I have also been told that cyano does not like flow which is why I try to keep the flow high sometimes.

Any ideas would be appreciated... but not in the mathematical realm like formulas... I will be lost.

Thanks