As far as I can tell, my filter is about 15 years old and has never had the sand replaced. it is not working efficiently as I have to backwash weekly to keep the pressure low and has actually sprung a couple leaks in the plumbing between the pump motor to the filter (supposedly due to the high pressure?) Also, air is bubbling back into the pool after the equipment shuts off. Is this a bigger issue or does the sand need to be replaced? If I have a new filter installed, what's a realistic price? My pool is standard size -somewhere around 24*12 and 4-5 feet deep. Thanks!