At one time I had a DC skimmer. I thought if there was a way to detect the height of the bubbles, you could have the reef angel adjust the skimmer pump so It would stay at a constant height. I found these on ebay. Would they work? The fiber optics are through beams and you could drill them into the collection cup. You would also need their amplifier, too.
http://www.ebay.com/itm/KEYENCE-FU-77TZ ... Swrx5UXAZQ
http://www.ebay.com/itm/New-In-Box-KEYE ... SwyQtVhR6x