Why did my fish die?

Question

my black ghost knife fish ( black thought ) just died after a water change. he showed no signs of sickness and about a month ago showed signs of ich but b4 i culd get around 2 the store it was as if it was gone( i noticed it on a monday and friday is payday) but when he died i saw a spot on his belly that looked as if he was injured or he was scratched by the bamboo decorations i have in the tank. also i have two red dwarf gourami's that live in the tank and also have been suspected of killing two angel fish by biting there fins until they just couldn't swim anymore..also those two lil fish are greedy, by eatting both flakes and blood worms( larve) and leaving the scraps for black thought

so if possible please give me sumtype of help on explaining if i did something wrong or what before i make a run to the pet store for another bgk or anything else

Answer 1

Maybe the water was too cold or hot. They do that sometimes.  

Answer 2

yeahh you might need a heater the water could of been a shock to him, such as here in hawaii its always warm yearly but in winter our waters turn pretty chilly so we need to bust our our heaters for november to january.

Answer 3

my mother had gourami's and other fish and the gourami's kept nipping at the other fish so that might help either get another tank,keep the gourami's or separate them some how.

Answer 4

If the Knife was showing signs of Ich and it went 4 days without treatment, it is very likely the killer.  The most vulnerable part of the fish, and therefor the most quickly infected, is the gills.  As the parasites mass here, they reduce the amount of space the fish can draw oxygen from the water (similar to having fluid in your lungs), making it harder to breathe.  If the infection is really set in, it will suffocate the fish, especially in warm, slow moving water, as warm water holds less oxygen, and without surface agitation, there's less contact time with the atmosphere.