death over night

pls tell me why!

my 3 cow fish, 1 blue tang and 1 camel shrimp are dead over night in less
then 8 hours. when i last see them, they were as alive as ever. i fed them
with defroze brimp shrimp just before i went to bed and when i woke up the
next morning, i am being greeted with 4 lifeless bodies on the bottom of the
tank. they were eating as usual when i last fed them.

but surprisingly, my mandrine and scooter blemy, star fish and fire shrimp
are doing fine.

i suspect it's my liquifry marine (by Interpet - liquid food for inverts and
corals). cos after i feed them, i add a dose of liquifry marine. and i
notice a foul smell from the bottle and also the liquidfry marine appeared
cakey. it use to be smelless and very watery instead of cakey. i have have
used this product for almost 2 months untill this morning.

can some1 pls tell me what or why cost the death of my beloved fish.

sorry for the long post.