what are your water parameters? mainly nitrates.
the pink cyanobacteria will feed of the nutrients and nitrates in the water, soak air-stone in hydrogen peroxide to clean, replace air tubes with black or green piping.
unfortunately cyanobacteria is quite common and quite annoying to get rid off, ways to get rid off are increased water flow (not suitable in axolotl tanks), change clarity of pipes (found to be more common on clear tubing etc..), because it is microscopic wiping wont remove all of it but hydrogen peroxide will destroy the cell structure, reduce nutrient/nitrate levels, reduce lighting / use blue night light.