Platy, Swim Bladder Problem?

[Bath Tussue]

ever since yesterday, one of my platys had been staying around the bottom of the tank.
it seems like it can't float up.
it would swim around dragging its belly on the gravel.
since yesterday, the highest i have seen it swim is about 3cm off the gravel.

it is also bloated.

water condition:
ammonia: 0~0.25ppm
NO2: 0~0.25ppm
NO3: 5~10ppm

the only recent change to the tank is the addition of an air stone.

 

[WILDER]

How long has the tank been set up.
How many gallons or litres is the tank.
How many fish and which type.
Being bloated epson salts baths help draw the fluids out.
Shelled peas and daphnia.

 

[Bath Tussue]

up for about 3 months
20gal
10 each of angelfish and swordtail (over stocked by the 1" per gal rule, but the LFS said its okay now since the bacterior coloney is established)
plus another platy (this one female. the one with the problem is male)

how much of that salt should i put in the tank?

 

[WILDER]

The tanks really overstocked shouldn't have more than two angels in that tanks size.
You will never get good water quality as the filter not coping with the load of fish in the tank.
Water change, and add another filter till you can rehome the angels.

Cook frozen peas for a few minutes, let cool down, pop out of shell. mush between fingers and add to the tank.
Frozen daphnia very good for digesting a fish food.
http/www.fishjunkies.com/Treatments/salt.php