Originally Posted by jfhrtn
In my 29 gallon I have had the same thing. Especially since it is still only 2 months old and is still getting established. I believe it it's just a type of algae or maybe diatoms. I had more diatoms than anything in my intake tube. I just use a pipe cleaner just like the one in the pic below to get all the gunk out to make sure it doesn't clog the impeller or the media. I hope this can help you out
Thank you for your suggestion , today I cleaned up my filter's tubes. I used this method this method
. After cleaning I used sera nitrivec for getting bacteria. And I'm also thinking cover these tubes with aluminium foil to prevent them from light.