we have been getting less and less water pressure over the last few weeks..we thought the filter was plugged and took out today...still no water pressure..when we turn it on at first it has good pressure..then after a minute it gets less and less till it gfoes down to a drip...i noticed the tank was down to 20 psi....my husband then put some air into the tank held at 40- psi...as soon as i turn water on goes down to 15 psi...help please...we have an amtrol wellxtrol tank..thanks tina