Platys are a brackish fish meaning they like a little salt in their water,
If only they need, every platys don't need. You shoud ask it from your pet store. Although fins clamped could be caused water without salt or just too soft water.
platy
- basic, hard water
- need salt if they has been grown in brackish water like LesGerber wrote.
gourami's
- what gouramis?
silver sharks
- oh boy! You need Ocean
Although I think you are talking about
Balantiocheilos melanopterus and in english it's bala shark or tricolor sharkminnow (I think)
- at the very least 500 liters, 2m long aquarium, the bigger the better. It is very fast swimmer and quite a big fish.
- slightly acidic, soft water
zebra danio's
- slightly acidic, soft water
head and tail lights
- Head-and-taillight tetra ->
Hemigrammus ocellifer?
- slightly acidic, soft water
harlequins
- acidic-slightly acidic, soft water. (pH 5-7)
neon tera's
- acidic-slightly acidic, really soft water. (pH 5-7)
and other tetra's
- what tetras?
Check:
- pH, GH, KH, NO2- and NO3- and of course temperature