Hi Gail,
I am currently running an HOB system. At first I ran into "bad stuff" issues.
How much live rock do you have? I think it is critical to have as much as you can with an HOB system. As soon as I got to the right proportion my "bad stuff" was easier to get under control.
I can only speak from what my experience has been and I hope others will chime in as well :)
Do you have a protein skimmer? That was the first piece of equipment I added that really helped! Remora C is a great product.
Flow... how much water flow do you have? With HOB systems it seems like you need to really pay attention to that and add a powerhead.
There are some great tips on the board to help control algae. I read through all of them and tweaked things here and there to help. I had a TON of hair algae and some bubble algae too. An emerald crab, a great clean up crew, a lawnmower blenny and a couple of tangs seemed to whip my algae problem within a month.
Peppermint shrimp - I went through 5 of them. Took care of my aptaisia problem pretty quickly. I saw two pop up the other day that I used aptaisia x on just because I didn't want to chance a new problem.
From what I hear... you gotta get rid of that majano immediately. - throw away the rock??? I would seriously consider that if I found one in my tank. I am sure there are less violent answers that someone with experience can help you with.
OH! to answer your HOB refugium question.... I have considered adding one to my system for a while. However, I found that throwing the chaeto in my display behind the rock wal has given my tangs some fun stuff to much on all day... even the crabs dig through it. And honestly, it isn't ugly because most of the time it stays behind the wall only bouncing around when my yellow tang decides to play chase.
Maybe that really didn't answer your question the right way. You do have options!