A fighting conch Strombus alatus could grow up to 4 inches, while a queen could grow much larger and probably not be suitable for your 55. We love our two fighting conches and they keep the sand spotless.
I have a Fromia elegans and I have the same concerns about him as gtusd. The view in the hobby is that they are film algae and detritus eaters. According to Ron Shimek, the marine biology view, apparently based on only a few observations, is that they are probably sponge predators. I too...
If your goal is to establish a conventional Deep Sand Bed (DSB), then you should not "clean" the aragamax, as this would eliminate much of the smallest diameter particles that form an important part of the DSB. Search threads on DSBs, and read articles by Ron Shimek.
Hector
I have a 90G tank, and a Kent MAX25-which puts out maybe 10 or so gallons a day, which is adequate but I should also have got the 50 GPD since they aren't much more expensive.
Cleaner shrimp are hermaphrodites-both male and female ate the same time- so any two can be a mating pair. It is common for them to produce eggs in aquaria but difficult or impossible to raise the larvae to adults.
The GPD that you will actually achieve will usually be much less (roughly half) than the rated GPD, because at colder water temperatures (ie water from a typical cold water line) the RO unit is less efficient, so keep this in mind when choosing your GPD rate. I have a Kent Marine and am happy...
There is a neat little book by April Kirkendoll called "How To Raise & Train Your Peppermint Shrimp - A Hobbyist's Guide To Raising Saltwater Aquarium Shrimp From Egg To Adult". She describes in entertaining detail her experiences in raising (and selling for a while) Peppermint Shrimp, Lysmata...