It could possibly be two different problems in one package - an algae forming over a biofilm containing Serratia marcescens (the pink bacteria that grows on damp/wet surfaces in bathrooms and food containers). If it is S. marscescens in the tubes, it would be gram negative, so wiping it out without murdering your nitrogen-oxidizing bacteria might be tough. Plus, it may come back if conditions are right (it's an airborne bacteria). It likes phosphates, fats and stagnant water when growing in bathrooms, and doesn't care about light (I don't know if it likes those conditions in a tank, but you may want to check your phosphates, if you already have the tests). It acts as an opportunistic pathogen for people and other mammals, though it can only infect us if we have a VERY weakened immune system. It may infect your fish if they are already sickly, since I'm seeing a few studies that pop up naming it as a fish pathogen, too.
Not sure if that's what it is though, but giving you another possibility. Don't freak out and nuke your tank, I'm pretty new to aquaculture, so hopefully an old-timer will chime in and say that it can't be that stuff, or isn't dangerous in an aquarium setting.