bleaching diffusers work well for me. just be sure to let it sit in a dechlorinator before putting it back in the tank.
another method i've tried recently was during my last water change. i raised the diffuser to the top of the aquarium and poured h202 onto the disk. it sat for about 20 minutes. it works okay but not great. there was a huge improvement but there was still a hint of green on the disk. imagine the algae becoming a bit faded. overall though, i like this method because its easier than taking the diffuser out, letting it sit in bleach, letting it sit in prime, then putting it back into the tank.
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