Dirt flow back in through return jet

I am getting dirty water sucked up by vacuum line which I am doing myself.It sucks up fine but just blows back through the nearest port. 13 k fiberglass pool 4 cqrtridge filters any help?

You have a problem with your filter. Either the fabric is torn in one of the filters or the filter is no longer seating properly in the housing and allow debris to get by. Remove the filters and inspect for damage.

I did just that...what I found was the filters had a slight bend on the bottom where it seats. I took them all out....cleaned again and reversed where the filters were sitting. Works fine now thank you although I think its time to order new ones. Thanks Dave