please help?!

i had a tank for a while and i had over stocked it so i moved to a bigger tank, before moving the fish to a larger tank, i had a blackmoor that wasnt well-this died in a seperate tank,
but since putting the other fish in the larger tank l;ast week,
iv lost one and i think im about to lose another.
is there anything i can do to stop it ?
the ammonia is at 0 and nitrite at 0.05, im not sure of the nitrate, but i know there are 4 plants in there so i dont think the level will be too high ,

the thing is , 4 of the fish were from one pet shop, another and the loach from another shop and a fish my partner had already,
its 2 of the ones from the first pet shop that have died and the one that is ill now is from that same shop- the others all seem to be fine?!
then again so did the others?!

what can i do to stop them dying ?
im unsure of if it was the petshops water being different to mine as they were 2 seperate types of fish from 2 seperate tanks ....

but it would be great if you could advise me asap on how to save my balckmoor.?

thanks

iv got a liquid nitrite tester and a strip ammonia.
but the fish i said about is now sitting on his side on the bottom of the tank,
iv noticed with the all that they seem to of lost frequent use of one side of their body before dying?!

but what do i do withthis fish as he looks as if he is almost gone, and i can stand to see him just sat there slowly dying?!

How long was the larger tank up before you relocated?
i got it on the monday,filled it and left it to stand until tuesday night then added the fish along with all of the water from their tank as it added up to about a 5th of the water in the larger tank.
what are you using to test?
api test strips at the moment and interpet liquid nitrite tester
how did you acclimate the fish?
there was a heater in the larger tank to i left it on whilst at work and then when the temps were the same i added the fish/
but with several fish dying after the move I would suspect that there is some water quality issue going on.
i did an 80% change yesterday, ill test the water now and if it reads for nitrite i will repeat it again today!

what is nitrite?! i know its from the ammonia going through the filter and changing, but why is it so high? is it that the filter is too big or just ............?!

I don't think the nitrite level is all that high at this point, but it sounds like you are in teh middle of cycle (even a mini cycle can kill fish).
how do i 'fix' this?!
would it be best to move them in to the smaller tank and re start the cycle in the larger one?
i actually dont know how to cycle, ive read the post on here but i still dont understand.



thanks for your helps!!

its just the ammonia thats a test strip. and after buying these i can afford a liquid one just yet. but my main concern at the mo is what to do about this fish i have half dead at the bottom of the tank ...........
do i just leave him to die slowly or do something or what lol ?!

i dont think it hasd eaten for a few days as its just floating there, side on, its struggling to keep up right, his tail is drooped to the bottom of the tank and hes just there side ways .............barely able to move?!