Cant really tell from the picture, since its in the shadow, but if it is bubble algae if you can take the coral out of the water into a separate container, simply remove it with a tweezers and then rinse the coral in a third container and put it back to your DP.
if you cant take the coral out, grab a tube remove it with tweezers but make sure to suction it when its popped.
Repeat it as necessary
Whats your water parameters?
When equipment begins to show rust is when I normally see it overrun. Check all components for any signs of rust, from hose clamps to screws that hold your canopy together. If it is continually growing, you must be unknowingly feeding it. Check your water with a TDS meter and see if that is the cause.