What's causing this backpressure spike and vibration?

[shellsingleton]

A big concern of mine right now is how my backpressure gauge on my sand filter will now jump to 30psi after a few minutes of operation following a backflush.
I'm backflushing daily while I work thru a shock cycle to rid myself of an algae bloom, and it just consists of a 3-5 minute flush whenever I see it at 30 psi or more. I will flush for about 2 more minutes once the water clears.
It usually drops down to about 20 and stays there.
Now it pops back up to 30 after a couple minutes.

I bf'd 3 times this morning to get rid of it, but it's still happening.
And it has developed a vibration in the plumbing that's strong enough to see the 2" PVC pipe moving.
It has rattled the bottom screen loose inside the (empty)automatic inline chlorine feeder.
:05 later-
I just walked out to check on it and it's back to 20psi w/no vibes. So it's not a constant thing. Great?
Could it be chatter from a checkvalve or a valve actuator going bad?
What about small amounts of air in the system? You can see some swirling bubbles under the pump skimmer's lid. I figured it was caused by cavitation from the impeller?

 

[mas985]

Dead algae will block a filter pretty quick depending on how bad is was. So the high PSI is probably due to the dead algae if the PSI drops after back flushing. Just keep back flushing until you have cleared the algae from the pool.

The air in the pump basket is more often than not a small air leak in the suction side. Pump lid or valves are usually the source.

As for the vibration, does it only occur at high PSI?

 

[repair_guy]

For a sand filter, get a product from SeaKlear called filter cleaner. You add it to the filter and let it sit for awhile. Then backwash. It will get most gunk from a sand filter. Also, you may have a layer of debris on top of he sand bed.