Read some of the articles on water quality here..
however...brief and skinny:
it is detrimental for long run because softened water has many trace mineral and electrolytes fish need being removed as well as bad stuff. And it buffers poorly while means a swing in ammonia level or Nitrites can be fatal fast.
Add to that the most the species you have like thier water on the hard side of 7 and you get health issues. The fish will never be at their most colorful and vital, as well as possible unexpected (if your were not aware) death.
you have one brackish livebearer(=messy and likes it with salt)
you have one fresh water livebearer(=messy amd likes it way fresh)
What I know of mollies and platys is above. That is it
and you have a goldy
(=messy x10 and likes some salt and cooler temps than others )who will out grow that tank just by itself.A single oranda should be in a minimum 35 if that gives you any idea. And comets and feeder types need MORE space.
Goldies should never be mixed with most other species for very long.
They can ruin water quality if not in a huge tank, they are oxygen hogs which is the biggest reason they need so much space (mess alone can be filtrated or changed out) and the warmer the water the less oxygen there is. Also if it fits in a goldies mouth. It will likely eat it, so smaller gravel is not good. they eat many plants. And small tankmates. Specially carp bodytypes and koi. ^_^ And PS..golds do not STOP growing to fit a tank size..it can stunt and slow their growth because the lack of good water, but they WILL keep growing. Any time you here a retail pet store employee talking on ease or convienience of a animal? Think the stereotype snobby gay clerk telling the fat lady the prom dress with lace and bows is "SoooYooouuuu!"
And think this, if goldfish in small space (bowl/10 gal
) are a good thing..how come the sitcom stereotype goldfish ALWAYS ends with a burial at sea?
thread has SCADS of info on many fish and water issues. Specially goldie info, links, opinions, etc. Easier than going over it all again.
One of the livebearer fans will tell you why platys and mollys , while
socialable are not the best mix.
Hopes this helps you start
sorting your muddle.