I have a tube that connects to the top port and use it as a fill line. I keep the water about 2 inches, the rest is filled with air. I don't have the other end capped, or at least not tightly enough to create a seal. I figured it's probably leaking due to excess pressures though.

Is it bad to fill the res all the way out though? Like I said, If I don't keep it topped off a whole cloud of micro bubbles develop, and I know that'll lower my cooling efficiency.