I just posted my opinion on this same question yesterday in another thread. The thread is located here:
https://www.livingreefs.com/hob-skimmer-and-refugium-t22457.html
Copy/paste from that thread:
I've used a few different HOB refugiums with the built in skimmer. They work fine.
Smaller:
http://shop.aquatraders.com/Hang-On-...in-p/43016.htm
I have that one ^^^^^^^^^^^ and used it on a 10g fraq tank for about a year. Recently moved it to the new 29g frag system until I save up the cash for an in-sump skimmer. It works good. Supply your own pump. I like the M1200.
Larger:
http://shop.aquatraders.com/Hang-On-...in-p/43017.htm
This is hanging on the back of my 30H display:
CPR Aquatics Aquafuge Large W/Protein Skimmer
I like that one a lot. ^^^^^^^^ Fits perfect on the back of a 30H or a 20H. Was 1/2 that price when I bought mine. Acrylic prices doubled in the last year.
The CPR is nice. But it's no better quality than the Aquatraders IMO. Well......... maybe it IS a little better quality, but the price makes it not worth it to me anymore. They are nice. But they ain't THAT nice. I bought mine when they were 1/2 the cost I see advertised today - so to me - I'd NEVER pay the price they are asking today. No way I'd pay that much.
I have 3 CPR refugiums. The first is the small HOB without the skimmer. Then I bought the small HOB WITH the skimmer and loved it. The larger model 24" wide HOB with skimmer just BARELY fits on the back of a 20H or a 30H. You have to turn the inlet tube over to get the powerhead on there, but it's not a big deal. I have the CPR aluminum PC lights for each one.
I have the smaller Aquatraders model. It's not bad quality, if you can do a couple very minor mods yourself.
The cup fit was pretty sloppy on mine. The collection cup had 1/8" gap on one side and 1/4" gap on one end. Some of the bubbles go right past the outside edges of the cup. I fixed the fit problem by cutting some 1/8" plexiglass and gluing it into the refugium frame. It just takes up the space between the cup and the refugium frame. That mod alone increased the skim by 25%. I did this while it was running on a tank. Took 5 minutes. I measured the width of the refugium frame where the cup sits. Figured out the bottom of the cup had to sit a couple inches below the bottom of the top frame rails. So I cut a couple pieces about 4" long to fit on the side and one end of the cup. Unplugged the pump - let the water drain down - scrape any coraline off the sides real quick - rinse it with tank water - dry it off - slap the super glue on the pieces of plexiglass and slip them in the refugium frame. I ended up using a single piece of 1/8" on the long side and 2 pieces on one end. Glued it in with medium cyanoacrylate (CA - Super Glue) and let it sit for 5 minutes. Slid the cup in. Plugged in the pump. Fits tight now all the way down to the very bottom of the funnel inlet. Perfect! Now most of the bubbles go up in the cup.
It also has a VERY sharp 90* degree angle from the funnel on the cup up into the straight part of the tube. It's a hard corner and very rough. I'm positive it would smooth out the bubbles if I angled that and rounded the hard edges off a bit with some sand paper or a dremel. Would take 5 minutes but I'm too lazy right now. I'll get around to it.
I like to run about 300GPH pump on all these refugiums. It just seams to work. The MJ1200 makes a great pump for these. But I've been searching for a needle wheel pump I could use. I'll bet a needle wheel pump would really make any of these skimmers go nuts.
:Cheers:
