loss of skimmer suction and blow back in skimmer

Hey everyone i have a 30,000 inground pool with a 1hp hayward pump and a sand filter. I started the year just fine was able to run my automatic vac thru the skimmer and it would go wild. I recently changed the sand in the filter. After that i was getting sand in the pool from the returns but could still use the auto vac very well. I opened the filter took out the sand and had a broken lateral that i replaced I have also replaced my pump seal. I can still vac with a hand held but not much suction but does the trick for now. The automatic vac wont run at all and i see air in the pump when i close the main drain and run off the skimmer only, also get a lot of air bubbles out of the returns with just the skimmer running. i have two lines that meet before the pump one main and one skimmer. I have also been experiancing a lot of water shoot out of the skimmer when I turn the pump off. Anyone know why this would all of a sudden start happening after changing the sand?

You are describing problems that sound very typical of a suction leak, which allows air into the lines ahead of the pump.

There's a fair chance a valve or some other piping got turned, bumped or otherwise disturbed, and is now leaking. Or, it could just be a damaged pump lid or lid O-ring.