Pool pump blowing bubbles

Pulled the cover off the pool today and began the opening process. It's an above-ground pool with a Hayward DE filter. The issue I'm having is this: the pump return into the pool is blowing a constant stream of bubbles. Pool water level is correct. There are no water leaks from the pump, filter, or plumbing, and the filter canister has been bled.

Air is being introduced somewhere on the suction side, and only when the pump is running; I determined this by insuring the pre-pump basket canister was full of water, then starting the pump - after ~1 minute, the canister is barely half full and I can hear and see air through the system and out the return. This is repeatable. With the pump turned off, the canister does not refill with water until I crack the cover open, releasing the trapped air; it then fills normally. The hose clamps are tight, and the canister cover O-ring appeared intact and was treated with that thick silicone (?) lube used for pool plumbing.

The only thing I can think of is that the O-ring may be leaking under suction only - that's first on my list to replace. If that doesn't solve it, however, I'm out of ideas. Any thoughts, all-knowing GRM hive?

I have nothing constructive to add, however, 

Do you know why Michael Jackson was asked to leave the Zoo?

I think the o ring is where I would start.  Is there any obstruction in the hose on the suction side?  

rustyvw said:

I think the o ring is where I would start.  Is there any obstruction in the hose on the suction side?  

No obstruction that I'm aware of. It's a short run with no kinks, and when I pop the cap off the canister refills very quickly, so it seems to be flowing freely. I'll double-check it when I pull the cap to replace the O-ring.

And wheelsmithy, no, I didn't know, and I wish I still didn't.

Check the return o ring under the top manifold of the filter grid. They like to fall off or roll.

Other thing to check is the auto air relief valve if you have a microclear de filter. They break all the freaking time.

There's a suction leak somewhere if you're getting bubbles. If you're sure it isn't the pump lid, manifolds, or valves then the inside of the filter is the next place to go.

In reply to The0retical :

I don't think the leak can be in the filter can, as the air is making itself apparent under suction on the suction side of the pump, which says to me that's where the air is coming in (feel free to correct me if I'm missing something). I'm trying to narrow the suspects, though if the O-ring fix on the cap doesn't do it, I'll have to widen the search.

Another vote for the o-ring. 

In reply to 02Pilot :

If it's presenting in the pump probably not.

It's probably the pump lid o ring in that case.

Have you rebuilt the Jandy valves recently (or greased them if they're not the neverlube variety)?

In reply to The0retical :

I don't have any such valves in the system. The only valve is for the backwash out of the bottom of the filter can. There's a one-way valve in there, but it's totally contained within the filter can; the can itself is only a couple years old, so I'm hoping it's not part of the issue.

The O-ring seems to have resolved the issue. Thanks all.

And I spoke too soon. The situation is improved - less air is getting in, so the pre-pump cannister is staying full enough to keep the outflow strong - but there's still some air getting in from somewhere. Next step is going to be to inspect the cannister closely for cracks; I checked the cover (which holds the O-ring) and it seems fine.

FWIW, I had a very slow air leak one year when I managed to pinch the o-ring in a union while assembling said union.  The o-ring was more like a "Q" than an "O".  Took me forever to figure that out.  It was the union between the pump and the Jandy valve (on my particular installation).