Is that a garden hose in the filter? Were you doing a sand deep clean? There have been occasions where the garden hose was pushed down too hard and damaged a lateral. But what about wind in your area? It's been extremely windy down here making my pool look messy. Easy way to check is place a thin sock or nylon over a return jet or two and see if you catch sand. If you confirm sand, it's a no-brainer. You have to open it up, empty the sand, and pull the laterals out to see if one came loose, got cracked, or if the hub connection is the issue. But save the sand. Scoop onto a tarp or something since sand doesn't just go bad.
