Cool, colonial polyps.

Nikki says they are a pest, but in my tanks they have never multiplied, but only help filter the water. I can't remember their name.

Aloha,

Mark 

Do you mean they have multiplied and caused trouble for you?

Though they look just like the pic, it's also possible that the ones I have had were a different species.

One thing I know is that when "parameters are too good", as you said, with natural sunlight and such, many different organisms grow robust and form competing populations. I have always tried to make my tanks support a large variety of life. On the other hand by the way they are set up and maintained, some reef tanks simply cannot support a more complete ecology of many competing organisms. New tanks are most often in the latter category.

to illustrate my point, below is a pic I took of a small tide pool on the west side of the Big Island of Hawaii. Nice Aiptasia and hair algae, right? Butterflyfish and Tangs are very common in Hawaii, but they can't get into these small tidepools. Here Aiptasia and hair algae grow and multiply undisturbed. The Aiptasia spawn and the algae produces zygotes which wash away to the surf zone by the action of crashing waves. In open water they attach and start to grow until snacked on by a passing Butterflyfish or Tang (as seen in the 2nd pic in the same area).

Aloha,

Mark