protein skimmer help

I have a red sea reefer 350 g2 tank (75-gallon display, 17-gallon sump) and I'm shopping for a red sea protein skimmer. My LFS has a sale on the Rsk 600 AC for $400 and the Rsk 300 DC at $415. I don't know what to get between these two because I heard that oversizing your protein skimmer is bad...

Got this magtool skimmer off eBay that was listed as Brand New, fresh in the box, cool specs, the whole deal... Paid 73.27 total (I know this wasn't a good idea to begin with, I don't even remember putting a bid in). Look at the pictures, they're self explanatory. Contacted the seller and was...

I have a reef octopus 1000 protein skimmer and I turned it off in order to do a water change and now it's making a lot more microbubbles than before. I've had this since March. I tried tuning it up and down, but the microbubbles are still there. This photo isn't my protein skimmer, it is a...

I had my protein skimmer, (reef octopus hob 1000) and it was working just fine, barely producing any microbubbles, but I turned it off to do a water change just now and now it's producing microbubbles a lot. I even shut off the tube (the one that allows air to come in) completely and it still...