Pressure problems after sand change and opening

We had our pool company change out the sand in our filter, 2 days later we opened our pool ourselves for the first time. It went well everything seemed to be working. When starting to vacuum winter debris from bottom it just wasn't vacuuming well. It was a little dirtier than usual but my vacuum usually is pretty efficient. I usually don't have to backwash but maybe twice on the opening vacuuming. This time I did it 5 times. Did notice that my psi is running at 20 -25 while in the filter position yet in backwash or rinse it runs 12-15 psi. I'm thinking something is wrong with the sand filter. The service guy says he expected to use 3 - 50 lb bags of sand but put in 4 he also said he only took. He only took out what was dirty as he thought he may not enough sand. Any thoughts?
 
Hello, the problem is my vacuuming is not working well. My returns are strong. Why is my vacuum not as poweerful? Usually the suction is great, but now this year I had to close 1 of the skimmers and drain to bring the suction strong enough to clean dirt and mostly worms. I was told in the beginning that the psi should be around 12 mine is running 20 - 25. Is that ok?
 
Maybe its time to deep clean the sand filter to see what went wrong, here is how, Deep Cleaning a Sand Filter. Or have them redo it.

Please add your state or country to your location in your profile so it shows up over there <----, climate is often an important factor when we help you with your pool.
 
Welcome to TFP. As previously stated, you very rarely ever have to change sand from a sand filter unless performing a Baquacil conversion. Deep cleaning is all one should be doing to clean the filter. Sand does not go bad.