I'd start there and make sure it has approximately 25% less pressure than your pump is set to operate at. That info should be on the pumps rating plate if you don't know it already off the top of your head.
We just replaced outs. The pump would cycle quickly so I went to check the bladder pressure and found water in the bladder. Went to Lowe's and paid $39 for a new one (2 gallon).