We've had this problem where the toilet bowl water level won't go all the way up as far as it used to after flushing. It only fills to about 2" to 3" from the hole in the toilet. Do we need to replace the bulb in the tank? We tried adjusting the stem on the valve. It adjusted the level for a while, but water kept running and we had to pull the bulb up to stop it. Now, the water level is back to the low level again. Thanks for any help you can give....Rose