Whether that is the case or not, it does help. 10 times the amount is typical but for 10 times larger systems often so its the same ratio if a 300/500 is used on a mini reef 10-30G. Anyway, the HOB fuge is nice for growing pods as well and also for surface aeration if you don't have an overflow. More reasons to have one than to not just because of its limited size.

That's my $0.02. And yes, I have an AC300 on my 33g and I have mostly halimedia sp. in it as well as in the main display. Helps the pod population otherwise for my blennies.

it will just grow out in a big mat which is fine, as long as it's sucking up nutrients.

A good refugium should be the same size as the display tank. Refugium is a place to grow pods, or algaes etc, I used to keep 4 cleaner shrimp in my 40 gallon refugium and with all the larvae they put out my main tank got lots of food. Another thing with a refugium is, if you can, put it on an alternating light cycle, IE when your main tank is dark have your refugium lights on.

Keeping a refugium this size isn't practical for most people, I was lucky to have the room but I don't have it now. I'm considering a 15 gallon refugium over my 54 but I'm not sure I want to go that route.

Doug

I have a 23g sump/fuge over my 75g tank. There is about a 7-8 gallon section blocked off for heaters and skimmer, the rest is a fuge with LR, Cheato, and grape caulerpa. Before I tore it down, I had an insane amount of pod growth in there.... I had copepods, amphipods, zooplankton, mysid shrimp, etc... breeding it it. I have an interesting overflow setup and thus it allows pods to flow down into the tank more easily. I also found the nutrient export slightly beneficial since before I had a really bad skimmer, haha. I still wish I could have gone with a bigger fuge for more algae growing space.

Chris