True Siamese Alage eaters dying

I bought six Siamese algae eaters which have been in my quaranteen tank for
a week and a half.
After a week for of them have died in successive days. Prior to them dying,
all were very active and did not
show any visible signs of sickness. On the quarantine tank I feed them
antibacterial food and add some melafix/pimafix.
The other two left swim with the dwarf corys I have in the same tank.

Are these fish very delicate? Any suggestions why they might be dying?