This is my second summer with this pool. Most of the time I have the valves set so its running 50/50 skimmer/drain. While I was working with it last weekend, I noticed that if I turned the valves to favor the main drain, pressure bottomed out and the filter skimmer would fail to fill with water. although it looked like there was good water flow coming in. If I turned the valves back to 50/50 or 100% skimmer, things would return to normal. I did the shaving cream test on the exposed pipework and didn't detect any air being sucked in at the joints. I took a video of whats happening for better clarification.
I frequently ran 100% on main drain last summer and while the pressure would drop a psi or two over the skimmer, it did nothing close to what it is doing now. Does anybody have an idea of what might be wrong or how I can further troubleshoot?
Thanks and kind regards,