flame scallops require a LOT of filter foods to stay alive as well as being extremely sensitive to water conditions. they tend to not survive for extended periods in smaller tanks due to the lack of ability to feed enough without effecting water conditions. some successes have been reported for longer periods on tanks that run constant phyto drips, I have heard tell of a story that claims (I dont know if its substantiated or not this is just hear-say) success for over 2 years on a gorgonian species tank with a constant phyto drip.
generally the animals slowly starve to death over a period of months.
unfortunatly part of the problem is the truncated life span of the animal, its natural life span is only 3 years, . size will tell you the approximate age a scallop that is about 2 inches wide is already about 2 years old or more.