I have an in-ground pool and hot tub setup. I have noticed recently that the deep end skimmer is sucking a fraction of the volume that the shallow end skimmer takes in. I noticed this first when vacuuming the pool - I usually "choke back" whichever skimmer I am not hooked into with the hose to provide greater suction to the hose, and when I went to the deep end I noticed very little suction, even with the shallow end skimmer valve closed completely.
It is also clearly seen when looking into the top of the skimmer basket housing - when I close the deep end skimmer there is still a strong flow from the shallow end but when I open the deep end and close the shallow end, the flow slows significantly.
I cannot see any obvious obstructions in the skimmer.
Any advice on what could be causing this or what troubleshooting I can do to identify a potential problem?