Losing gph on my closed loop UV!

[Notsolostfish]

I have installed 5 months ago, a closed loop uv where the intake and outake ar eboth in the display tank, and a vectra s2 running dry. Yesterday out of no where i start losing gph. I usually run stable 532-535. And now im at 517-520. Is that slime building inside the pump and the pipes reduced gph? Is that a concern? Its an apex flow meter

 

[Stealthreefer]

Mine ends up about half the original gph every 6 months or so.
It's usually crud and algae buildup. I ended up switching to putting the pump in an HOB filter and only pulling pre filtered water into the pump and it didn't make much difference if any.
All my lines are in the light and clear so there is definitely build up of algae that starts building up clogs.

 

[Notsolostfish]

Mine ends up about half the original gph every 6 months or so.
It's usually crud and algae buildup. I ended up switching to putting the pump in an HOB filter and only pulling pre filtered water into the pump and it didn't make much difference if any.
All my lines are in the light and clear so there is definitely build up of algae that starts building up clogs.

When do i start to worry i put the system together few months ago but didnt start using it till 2 weeks ago