Look again. There is one large bubble that’s about 1/2 across and maybe 6-8 inches long. That is not going to make any difference to how well the system is working. It’s cosmetic. The pump draws from the low point in the tube and returns it to the high point in the tube, so as long as there’s enough fluid to circulate, the pump won’t run dry. And the system would have to lose about 1/2 of the fluid before the laser tube itself is exposed. Most of the glass tube is the water jacket. The laser tube itself is much smaller, and it runs down the center of the jacket…