yellow, rusty thing

Im not sure if this qualify for Emergence. Over a month ago I posted here, that I have some problems with algae caused by overfeeding. Thanks to you guys problem is solved. Algae almost gone, mostly because larger water changes and GFO reactor. Thanks. Little concern though. Couple days ago I noticed some rusty color in my sump, huge and skimmer. It looks like from pellets from GFO reactor. Do you know why? I know they should look like boiling water and thats what they do. Maybe 50 gal/hour or even less. Or i run too much, like 1 1/2 cup? Please let me know. Right now I unplugged it. Thanks.

 

What reactor are you using?

I have foam inserts to prevent media from leaving the reactor and going into the tank.

 

I have a BRS reactor. I use foam too. Still somehow that rusty dust got out. Maybe that flow was too much...

 

GFO should not be "like boiling water"; only the top layer should tumble gently. You want to prevent clumping, but at the same time prevent it from grinding itself into dust.