Ive never tried one of those refugiums, but I read they work well if you are looking for an external setup. Powerhead placement is an issue for some models, if they draw from the volume in the refugium they can blend up copepods into mulch. If I had larger systems I might try an external model--could be retrofitted to work on a skimmerless 5 gallon nano that would hold a stocking density beyond belief...
they are not internal they are external. I dont know what HOB is because im am computer illiterate but if you want to know who sells them I know marine depot does.
I built a hang-on for around $30 to put on my 7 gal bow. it is working great. The only problem I have is that i used 3/16" acrylic instead of 1/4". It bows a little bit, but it's okay. And I can't take out the outlet, I used acrylic tube I had around, and its glued in place.
I went with the medium even though I was tempted by the small. I am putting mine on a 29 (upgraded from my 20L plan) I am setting up especially for dragonets. Now I am debating running 24/7 lighting on it. The goal being plenty of happy copepods = happy dragonets.
