Are you running your glow light 24-7? And if its in the sump, thats exactly where you want it growing. I had Cyano growing in my sump, I had my 40w compact flourescent running 24-7, it never went into the DT, but I cut down the light time to coincide with the DT light being off, Cyano gone.
Cleaning the filter with tap water isn't going to do anything but clean the filter. =) I don't think theres enough phosphates and stuff left behind to do anything.
If you want to leave the light on 24-7, yea, it grows everything more, because its all using the light.
As long as you've just got it growing in the Sump, I'd leave it alone, it will help strip out excess nutrients from the water, you just don't want it in the DT where its ugly. How are your water parameters? Phosphates and Nitrates?