I have a Sand Dollar Pool Filter. Today when I turned it on, there is no return pressure. There is no water rushing through the basket either. I have backwashed and rinsed twice. Any thoughts? Sorry if my terminology is wrong. I'm a first year pool owner. Had the pump serviced in December and sand replaced. Added a new Polaris then as well. Polaris is not working because there's no pressure. Any tips will be greatly appreciated.