Here is what I have on Sea Hares: they often grow to massive sizes some cases 1 m and a weight of 7kg. they are purely hebiavours and consuume vast ammounts of red green and brown algaes, as well as sea grasses. they produce a purple liquid like octopi as a defense mech.the often produce long chains of eggs up to 500,000,00 eggs ina space of about 6 months and often times hemaphoditic.
We had a bad HA problem in the LFS display 180. The hares we added cleaned a badly infested tank in just a few weeks. Customers were shocked at how quickly the tank made a come back.
We corrected the real problem (Bad RO membrane)
As far as negative impacts?
They tend to get eaten up by power heads and strong intakes.
Ours never knocked anything over or bothered any corals. They avoided crawling over corals and went right to work each night.
Not sure how they would fair in a high flow tank. They seemed to have a loose hold compared to snails.
The only other negative I guess is that when the HA is gone they may starve to death if not sent to another reef with a HA problem.
I tried one for my Lobophora Variegata problem in my tank. http://www.saltcorner.com/sections/guest/algaepage/Brown/scrollalgae/Lvariegata.htm
It was totally uninterested to it went back to the store after a week.
Thanks for the heads up. I know they are a ugly looking creature that move pretty quick and Remind me of Pac man eating algae. I also know at one time they were hard to get. My Sea Hare moves pretty quick compared to snails. I am going to have to put him in my sump soon. I think he is running out of food inside my tank.