Hi GuppyGoddess,
It is a horrible task to encounter when you think "but if i could just save them" and in the end they pass on.
But im glad you have toughend up, altho that does'nt make the situation better it does help a little.
With mine it started with my swordtail he started with sunken belly and was very lethargic and swimming weird it was kind of like wiggleing instead of swimming, then he past away around 3 days after starting with the sunken belly thing.
Next was 1 platy a few days later, same symptoms and immediately removed into a hospital tank with meds, the day after another
platy and 1 tetra, only difference between these last 2 was the tetra wasn't thin and emaciated in the belly region, the platy was.
They both went into the hospital tank and a couple of days later the tetra passed on, and yesturday the platy passed on
I'm still at a loss as to what and where my fish got the sunken belly thing from, i do believe its internal parasites
but not 100% sure where from, im kind of thinking and have narrowed it down to some bloodworm pellets i purchased from
ebay as these are the only thing i changed in my tank apart from an addition of 4 penguin tetras weeks before the outbreak
and these where quarantined for 2-3 weeks before going into the tank, thats why im suspecting the bloodworm pellets.
I hope this helps you, keep me posted
Regards
Scott