green water

[PapaBear]

Your water went from brown (dead algae from the UV) to green (no UV). That makes me suspect that you have always had a high nitrite/nitrate load feeding algae just as you do now, as well as other algae feeding minerals in your water supply.
It would be helpful if you tested ph/kh numbers as well. Ph morning and evening would be helpful as it will tell us how much the algae cycle is swinging from day to night. You will probably have ph reading 1 full point lower in the morning than you do in late afternoon.
Kh matters too since you are running a bead filter. They eat carbonates like mad and if your readings are low it will never mature without help.
Mickeys suggestion on splitting your bead filter outflow so part of the water also goes through the old filter is a good one. The UV will start killing off algae again, improve your solids removal and biofiltration.
Since it is winter the process will be painfully slow and I'm also betting you'll need to start adding Koi Clay to help remove nutrients from the algae.

[KoiCop]

Mickey (Mitten) is correct -- splitting the flow after the bead and plumbing the old filter back into the loop will sustantially improve your filtration. Best,