My All Gold Fish are dying virally

Hello to all.

I have a sad news actually, those who are pet lovers.. for them.

Bought total 15 Gold Fish around 6-7 days ago. and 2 Gold Fish were allready there in my acquiriam.

But now only 6 Gold Fish left among 17 Gold Fish. Don't understanding why they all are dying almost like viral affect has..(!)

Everyday 2-3 Gold Fish dying, today allready died 2. It's so pathetic for me.

All the Gold Fish's i bought were so lively, looking so much fresh and healthy.

But now, after bringing them in my acquiriam, the mass death started 2-3 days later.. don't understanding why they are dying in that mass way!! I have acquiriam it about 16-17 years now, but i never experienced this shocking thing.

All fish are now so lifeless, even not moving, like they are waiting for their death!! and some are floating in top surface of water like they are dead.


I have changed my acquiriam water and washed everything of the whole acquiriam, thought maybe it's water problem, but nothing changed..

Can anybody knows what actually happening in my acquiriam?? I am so dissapointed. Just watching them dying everyday, in front of my eyes, but can't doing anything rather than only watching.

Afterall I love them.

my english is not such good, otherwise i could explain the situation better.