Personally, I'd get rid of them before they multiply. I had a small patch in my tank and I left it alone. Eventually, it multiplied in that area and one day, an accidental bump broke the patch open and my tank was infested. I got an emerald crab, but he just made it worse. They break open the balls and eat the contents, but spores get released all over the tank. Eventually, I had to pull the liverock and scrub it down. Since it's on the glass of your tank, take the tube from your siphon hose, start a siphon into a bucket, and gently scrape the bubbles off the tank wall with the hose. Hopefully, the siphon will remove the bubble algae spores and all.