Molly fly, probably not suited to tank, what to do??

I've got a newly set up tank that after some cycling was ready to slowly introduce some critters, I got some cherry shrimp and an apple snail to start things off, with a look towards the borneo and hillstream loaches i want to introduce later.
Into the bag with the shrimp jumped a molly fry which until the last 24 hours has been a pretty active little chappie, using all the water table, gobbling up stuff and grown nearly twice it's original size in the week i've had it.
Last day or so, it's been moping about, hiding a lot more than normal, taking a rest on he bottom, more uninterested swimming about, nothing above the bottom 3" or so and the tail looks a little clamped.
I've done a couple of water changes, one mid week, one today, about 20%

water readings are on a strip, so only approx
No3 0
No2 barely worth mentioning
gh 10ish
kh 5ish
ph ( accurate with digital meter ) 7.8
Cl2 0
ammonia, seachem alert thingy, yellow, 0
130ltr tank
2 filters ( 8ltr external & 1.5-2ish ltr lid trickle type, stuffed with media in both )
good flow over rocks one corner ( for the loach ), lots of bogwood and plants elsewhere

The shrimp are going great guns, one of them is a proper swimmer, swims everywhere, weirdo, the others are cleaning like Kim & Aggie on speed!
The snail, i think he's narked at me after he got electrocuted with 12v by dropping the LED strip in the water next to him trying to adjust it, hid away for about a hour, seems ok, but will still hide for half hour or so sometimes, not the normal sleep at the waters surface behavior.

After doing a bit of reading it looks like mollys ( esp fry ) need salt although thats not the set up the adults live in at the shop.

The only change in the day before that was dropping the temp back to about 22.5 from 24c ( to suit the shrimps )
and a slow emergence of the dreaded surface film, thats now gone with the last change, and a surface attachment to the filter added to keep it gone.
i've turned the heater back to 24c

Mollys still hiding, in sight, but hovering in the dark and fin still looks a bit clamped, but it's being waved about too quick to tell.
heck of a beery belly going on, maybe just pigged out too much on Shrimp Cuisine??

Anywhos, is this tank suited to a molly fry? I won't have salt loving tank mates, and i don't know anyone with a suitable tank, even the shop.

Cheers, Phil.