Cloudy skimmer backflow and knocking filter

[bromion]

For background, my pool is fairly small in-ground and a pool service maintains it. I rent the house and the service people aren't exactly top-notch, so I am looking for advice so I know how to deal with them and the landlords.

Yesterday, we had some folks over for a pool party. The pump was running and the pool looked great. I checked the chemistry myself and everything was within ideal range according to my kit (tested pH, hardness, chlorine levels, alkalinity). A few hours later, the pump turned off (timer) and something disturbing happened:
1) The filter was making a loud knocking noise. For a while I thought it was a neighbor hammering or something so I ignored it. It sounded exactly like someone next door using loud tools.
2) At some point, a saw a cloud of particulates billowing from the skimmer return back into the pool.

I've attached two images showing the cloudiness in the skimmer and the cloud pouring back into the pool. When I noticed this, I turned the pump back on, which distributed the cloud, making the whole pool cloudy. Over time, it seemed to dissipate. When I turned off the pump again, the problem did not recur.

Anyone know what's going on here and what needs to be done?

Thanks!

 

[JesseWV]

The cloud looks like DE and/or fine dirt. For that to occure, something is causing back pressure. This causes water to flow through the filter in the wrong direction. It's effectively backwashing itself into the pool. Pictures of the equipment set up would help a lot.

 

[bromion]

I will take some photos of the equipment and post them ASAP. Thank you!

 

[duraleigh]

I think jesseWV is on the right track. What would likely cause that is a suction side air leak.

Air get's sucked into your filter and then the pump pressurizes that air. When the pump is turned off, the pressurized air dome in the top of the filter pushes the water backward and pushes the DE back to the pool.

There is an article in Pool School that describes those leaks and a little on how to hunt them down.....it can be troublesome.

 

[bromion]

Dave and Jesse,
Your response made me figure it out! The pool has a fountain feature that is run off the main pump. It is controlled by a manual gate valve. We had the fountain on when the pump was running, then the pump turned off with the fountain valve still open. I didn't close the valve until much later. This is probably the source of the back pressure which caused this effect. I did a little test of this hypothesis today, and the same thing happened with the fountain valve open. It hasn't happened with the fountain valve closed.

Thanks for the help!

 

[duraleigh]

Nice work!