I,
Either you have good flow or you don't...
If you have good flow out of your pool returns, then the cell or more likely the flow switch is bad.
If you have poor, or weak, flow out of your pool returns, then the most likely cause it that your filter is dirty.
I suppose you could have the cell in backwards... We have seen cases where the cell was originally installed backwards, and then the installer turned the flow switch backwards, to make it work.
As long as the flow light is Red, nothing else will work.
Thanks,
Jim R.