HELP!!!! bought a colony of firefish and they wont gain weight

[Tabbatha]

I bought a colony of 8 firefish 1male 7female,
females were skinny i thought maybe they just held or stress
but they dont seem to be gaining weight iv lost the male and 1 female
they are all active and eat very well always hungry
ill feed twice aday but still not gaining
i dont know what to do
should i feed more? could there be some sort of parasite?
please any advise could help i dont want to lose these fish

[sucker4plecos]

If fish are eating well, but not gaining any weight, there may be an internal parasite....... Are the feces long white and stringy....? "Jungle" has a few products for internal parasites - one being a food pellet.

[Tabbatha]

im not sure about the feces havnt seen one yet but ill look for white feces
and thank you for the advise on the jungle products