Ozone is a gas and will accumulate to some degree in the top of the filter. However to make sure this is a minor accumulation, the sight glass and metering needle valve must be set when the pump is working at it’s highest speed. On a multi-speed pump this may be the startup speed. Then when the pumps speed is lowered for normal operation the ball in the sight glass will drop down. This is normal, do not readjust needle valve at the lower speed. The needle valve is still set to the proper place and is delivering Ozone. Only set the needle valve after filter cleanings.