Suggestions will be accepted

[Alarmguy66]

My 180 gal is maxed out on fish, but my 20 gallon only has 2 inhabitants, an Arc-eyed Hawkfish who proved too aggressive in my 180, and a damsel that I kept in the 20 to give it some life. Ive always used the 20 as my qt tank, although it has turned out to be more of an observation and isolation tank. Nothing that ever went in it ended up being sick, and quite awhile ago I started keeping all my undesieables there (crabs, huge bristle worms, aggressive fish).

Since I wont be adding any more fish to the 180 in the forseeable future, I am trying to decide what to keep in the 20. A mantis tank is certainly a possibility, and one I am leaning heavily towards (If I can find one). The other is some kind of herbivore (the tank has LOTS of calerpa in it) that can hold its own with the hawkfish.

The 20 has about 40 lbs of LR, 20 Lbs of sand, a HOB filter, a 300 gph powerhead and 100 watts of pc light. No sump and no skimmer, so bio load must remain tiny.

So...the question is this. What ONE fish can hang in toughness with a Hawkfish, be hardy enough for this environment, and eats caulerpa?

Side question. Will the Hawkfish stand a chance with a mantis in the tank?

[Shoestring Reefer]

The hawkfish would probably be mantis food. Mantises are called "thumb busters" by fishermen and divers because of what they do to humans. So "it won't attack something bigger than itself" doesn't apply to them.

For a 20, you need something agressive but either small or that doesn't need a big swimming area. Something like a maroon clown, but they aren't herbivores. Many herbivores that will stick up for themselves are on the big side (like tangs), and caulerpa is not really the herbivore food of choice.

I think that looking for an agressive caulerpa eating herbivore for a 20-gal might be a little restrictive.