@ ZoddyZod
what is your tank size?
>>>> 55 G
How long has the tank been running?
>>>> bought it on 11th August 2011
have you cycled your tank?
>>>> if you mean washing cleaning after buying yes i did
what are the ammonia and nitrite readings from your tank? If you dont know these, buy a test kit very quickly.
>>>> dont have the kit will buy
What fish do you have? Do you know their names? I see goldfish and angels, but what else do you have?
>>>> sorry mate i dont know name of any of them just went to the shop and asked to put this this this this in tank
Best thing you can do right now is do a big water change (50% or more) - so long as you are using dechlorinator in the water first.
>>>> i have changed water like 70% everytime when 1 of them died
@ XeroTolerance
Okay there are tons of things we need to know. Answer all of ZoddyZod's questions. This is what I think happened. First of all you don't have a good combination of fish. Second you needed to cycle the tank. If that's the case than your fish probably died from high ammonia levels. Also adding 20 pairs of fish in one day is too much. If you did fishless cycle you still want to add your community fish first than add your aggressive fish later. It also looks like your tank may be overstocked. I doubt that fish tank is tall enough for angel fish. I also think that it is overstocked with just the goldfish alone, if that is what those fish are in the 3rd and 5th pictures. What fish are still living so we can advice you to what you need to re-home, if there is any that may need it.
>>>> can you please tell me good combination of fish atleast 4 pair of fish to keep in tank, i'll add now 4 pairs
all the remaining fish are dead