hey guys... I'm about to clean my sump, but the last 2 days or so I got this golden brown "algae" on my sump walls, mostly in the ref chamber. Are they dinoflagellates? I don't think they could be diatoms because I have a 2 year old tank and run phosguard that takes out silicates. Could it be...

I'm trying to figure out why my algae is turning white. Anyone know?