Help Fry acting funny an dieing

Hi Im realy confused my fry are now about three weeks old and have grown realy well some are around an inch already. but they have all suddenly become very dopey and gone off there food. also they are all at the top of the water with there heads poping out of the surrface. i have been doing half tank water changes every 2 days cleaning out all waste food and fesies. 4 have died in last two days

its a 30ltr tank with arond 30 fry
fulval 2+ newly installed with meadia from another tank. (i did this after them going dopy as othere pump was a little small)
no ornaments or gravel
all tests prove ok.
fedding zuccini, JBL pleco tabs,tetra prima and flake.
thay are on there own.
It has a air pump to but i ave turned it off as i was worried this was blowing smoke in. i have setup the 2+ to push are in as it has mostly sealed lid

I do smoke in the room that are in but it has never bothered any of the other tanks but all other tanks are 90ltrs or over having 30% weekly ater changes

i found a dead fly in there could that cause this type of thing. im about to do another water change and put some carbon in i got with new filter

Did this start after you turned off the air pump? Up at the surface with their heads out sounds like they aren't getting enough oxygen for some reason.

no it was befor i turned it off am certian there is enough oxgen in the water. iv got the air intake on the filter going and theres load of surface agitation. i have put the carbon fillter in now so ill see how it go's i also just did another 50% change and iv put a couple of the fry in another tank to see how they get on

sounds like youve over cleand the tank.
do you treat youre tap water.?? as it could be chlorine poisoning
if the fry are moping about then shooting to the top and twisting when swimming.
its new tank syndrome quick cure sqeeze a dirty sponge in the tank and leave it running dirty for a few days.

I'm with Deano on this one. Sounds like the tank is too clean and they are stressing out.

I would def get the airpump going again. more air the better!

Then i would leave it for a few days, only thing i would do it is to remove any fry that may die, as they will pollute the water

good luck with it

i paniced and moved them to another growing on tank. they are all fine now.

that works too

always handy having a few tanks on the go