im not flaming anyone, but my opinion is against "converted" fish. "fw" bumblebee groupers all seem to get nowhere near there full life, neither do morays. just the same the other way around. I wouldn't put pleco's in brackish water though just because they come from soft blackwaters, the opposite of brackish. ive seen plecos kept in brackish water and they swell up really big and develop huge boils as they can not pass excess water because their osmosis regulatory organs can not function. you can try it but im not sure on your outcome. some people keep them and have reported they are doing fine so far, but i havnt heard of an adult pleco in there for 10-20 yrs. o and some are more sensitive than others, commons are a very hardy species...