Look at your pressure gauge. If it is reading high, you have a clogged filter. Open filter and clean out or replace sand.
If it is reading low, you have a pump/ suction issue. Check the o-ring on the pump basket lid and make sure it is lubed and has no cracks. Check your basket for cracks. The pump impeller could be clogged. The pump may be pulling air in through a suction fitting or a small crack.
