We emptied the old sand out of the filter and there was no pea gravel at the bottom, it's possible the old owners neglected to put it in there. Should we put pea gravel down there, would it help?

unfortunetly all discrimenating labels have long worn off both pump and filter. There is a plate attached to the pump with a number. I am having a problem downloading a picture. The numbers on the pump read COL1081PSC motor RU, I'm sorry I can't give you more info.