Just switched the skimmer on a couple of days ago, tank is about 3 months old now. The water level in the back compartment is now at the correct height according to the instructions. I have removed the air valve and with the gate pushed all the way down the bubble height in the skimmer doesn't even reach the outlet where the cup attaches, even with the valve attached and adjusted it makes very little difference. has anyone got any suggestions as to why it's not right?