I ran a zoo med 501 on my 10 gallon planted tank & I know the flow is weak! I first started with a power head with sponge & a small fluval internal. Started having big problems so I went out thinking the 501 with the small fluval would carry the tank. (IT DID NOT) . BGA & green water at the same time while dosing dry ferts & keeping higher nitrates , say over 15ppm & not letting PO4 crash. What turned it all around took many changes. The BGA was over running the tank fast.
I changed lighting to 6500k 2( 15 watts fixtures) T8. Was 4200k. Next I tossed the small internal & powerhead, opting for Fluval 106, but I left the 501 zoomed along with the fluval. For other reasons I dosed the tank with flagil. An antibiotic which is for internal parasites , but I feel had a negative effect on BGA. Also 1 day accidental blackout by accident. When I turned the lights back on the tank was free of BGA & the water was clear. I added activated carbon to help clear the water more to pull out residual DOCs. The water after 3 or 4 days after the carbon was put in was extremely clear. The extra boost the tank got from the 106 blew away the Zoomed , but I left the Zoomed anyway.
Yes, flow is extremely important in getting rid of BGA. But you need good filtration & proper nutrients & lighting spectrum. Antibiotics could help also.On a final closing note I have noticed many people get this stuff growing on white fine sand as well. Most of the u-tube videos with BGA have white sand in the tanks. Something to think about. I had put some in my tank & the BGA seemed to like growing in those areas better. I have since removed as much as I can. 2 months free so far of BGA. Good luck