Help troubleshooting a pump/filter problem

[Gluggug]

So glad I was referred to this site by a friendly stranger at the pool store! I've been lurking for a couple of weeks as a first-time pool owner and the information here has been incredibly helpful, but now I'm stuck with a problem that came up earlier this week. I'm still a newbie so I'm going to describe everything I've observed in the hope someone more knowledgeable can set me on the right track. Quick background: I had to SLAM the pool last week due to algae starting to grow (I was out and my wife isn't comfortable with the chemicals yet). I cleaned out the filter during the SLAM and got everything back together without a problem. But figured I would do a final cleaning since the water was almost back to clear. Got the filter out and cleaned, but before I could put it back in the circulation system kicked on - queue much stress as I tried to turn it off and get the filter back in as soon as I could. I figured out how to turn off the system and took my time putting the filter back in. This is the point the problems started:

• With the pump turned on, the pump basket doesn't seem to be filling completely. At least I can see the water coming in which I don't think I could before. Instead I think it was always close to the top even with the pump on. Water is close to the top with the pump off
• The pump seems to be oscillating in pressure (high, low, high, etc). After a few minutes I can literally see the top cap of the filter shift up and down with the pressure. Not sure how this is even happening since the clamp is on quite tight. I checked the o-ring several times and it looks fine without any cracks or cuts. I don't see any damage to the filter or the filter container, nor is there anything that looks like it would cause a poor seal by the o-ring.
• There's an air pressure release on top of the filter (at least that is what I assume it is). It's releasing air pretty frequently (~15 seconds) when it never used to do that
• Turning on the booster pump for the Polaris makes the problem much worse and causes the filter to leak water pretty profusely at the top clamp. It sometimes dribbles water from the top even without the booster pump on
• When I turn off the pump, I can hear air being drawn into the filter cartridge by the seal. I don't recall this happening before either but I could be mistaken
• I tried running the pump without the filter in case it got damaged somehow, but there wasn't any change.

Unfortunately the filter pressure gauge was no good when we bought the house. I ordered a new one but it hadn't arrived by the time this all started. I should get it in the next day or so at which point I can see what is really going on with the pressure. Based on the symptoms and searching TFP, I think there may be a blockage somewhere on the inlet side. I have no idea how that would have happened though. Any ideas?

We had a neighborhood pool guy look at it today. He claimed the pump wasn't sized correctly and that he could put a new more powerful one in for $1000. All the research I've done so far points to him being wrong on both counts however (1 hp is probably fine for an in-ground pool without a spa, and I don't think this is caused by a defective pump).
Thanks for any suggestions!

Edit: Got a working pressure gauge on today. When I ran the pump it oscillated between 0-10 psi so my current thinking is there's a supply side blockage. I tried to backwash from the pump to hopefully clear anything, but it only seems to have made the supply side worse . There's only a trickle of water coming in now. Unfortunately I can't isolate the main drain and the skimmer. So, thinking about trying to snake out from the pump side and hope for the best.

 

[mas985]

Also, check the skimmer weir. It sounds like it might be stuck causing a vortex in the skimmer so it is sucking air.

 

[Gluggug]

Thanks! The weir is the flap in front of the skimmer correct? If so it doesn't have one, but I think I sorted it out. I backwashed again and this time tried temporarily blocking the skimmer inlets to try and force the water back through the main drain. Ended up seeing some cloudy water come out of both the drain and skimmer pipes. So, restarted the pump and so far so good. Pressure is maintaining around 7-8 psi, the pump basket is almost completely full while running, and no more leaks by the filter. Ran the booster pump for the Polaris for a bit an no leaks due to that either. Some air bubbles are coming out and the air valve on the filter is still going every once in a while, but I think that's just due to having so much air pumped into the system. Will keep an eye out but so far so good!