I highly doubt this is caused by your filtration although Im not impressed with the emporer 400 as hang on filtration goes I used the aquaclears on my 125 up till this summer when I upgraded to wet /dry.lets just say wet dry can be a pain in the butt constant top offs power failure if you dont have the proper size sump can overflow I add 5 gal of water to each of my tanks every other day.open tops dont help this ither. .the biggest question for you is how long are these fish in your LFS before you take them home?these fish go through so much stress and drama before they even make it to the LFS we all preach qt your fish for t least 2 weeks before adding it to the main tanks .well these stores are selling these fish within days of reaching these stores.most when purchased are already over stressed ,malnurished,improperly acclimated.if a fish wont eat in a LFS chances are its not going for you either.if you must go with live spend a few extra bucks buy some damsels no one likes them anyways for long periods of time.these fish are almost always braught to the stores wild caught unless it was a trade in.you are not their freind at this point and time you are their capture.in the amount i spend each week on frozen prepaired foods for all my tanks inhabitants it would be no more noticable cost to by damsels at a bulk amount.but if it the cost of a life you chose to keep captive isnt it worth the few extra bucks until it will accept frozen.if you inform you LFS that the purpose of the damsels is for feeders and you plan on buying a larger amount say 10 or so they may be very willing to give you a discount for bulk purchase.