I found chaeto is pretty cheap. You don't need a huge light. I use a 10 dollar light that grows it perfectly. A hang on back refugium is only 30 or 40 bucks. Another way is to reduce feeding or feed less frozen food and more flakes and pellets
It might be hermits? Do you feed your acan? Hermits will come up and irritate them. Also what light are you using? Sometimes too much light or light schedule may be off. If you’re concerned about refugiums prices maybe consider an ornamental Macroalgae like red ogo. You can check a lfs or aquarium club and see if someone is selling it for 10-20$ and wedge it into a rock of your tank. (Not necessarily the best solution imo, a refugium is always the way to go) but a cheap band aid for now. Also, dip your Macroalgae because whatever’s in someone else’s tank will go straight into yours if you don’t do a dip.
