Head & Tail Lite Tetras Dying

[ballzy]

Hi

I'm new to this forum and in need of some help. Yesterday nite just before going to bed i noticed one of my head & tail's was swimming at an angle tail slightly down, i sat and watched it for a while and other than that it looks perfectly well, it was swimming around ok so i went to bed. This morning i got up to find it floating around occaisonly trying to swim, i assumed it was dying so i took it out and sent it to fish heaven (i hope that was the rite thing to do?) Now another one is doing the swimming up thing, it's constantly flicking it's tail to stay up at the top of the tank but other than that it looks just the same as the rest of them.

I did my water tests yesterday Ammonia 0 Nitrite 0 Nitrate 20 and my ph is about 7-7.5
I have a 60 litre tank (55 litres water) occupants are 5 (was 6) head & tails and 5 neon tetras, tank has been set up for 4 months this is my sons tank and he's working away along his sticker chart for more fish!

Please help

 

[WILDER]

Sounds like swim bladder.
Does it look like the tail weighing the fish down in the water.
Does the fish looked bloated.
What do you feed your fish.

 

[ballzy]

Yes it looks like the tail is weighing it down as if it's taking all the fishes effort to stay at the top of the tank.
No it doesn't look bloated,in fact other than the dodgy swimming they look perfectly healthy.
I feed them flake fish food,altho on reading quite a few of the threads here i need to add a bit of variety in their diet.
So what shud i do?

 

[WILDER]

Frozen food and green veg. Frozen daphnia good its helps the fish digest its food.
Cook some frozen peas for a few minutes, let cool down and pop out of shell, mush between fingers into small peices and add to the tank.