Molly troubles

Question
QUESTION: Hi, i have only just purchased 2 Mollies yesterday to add to my tank with one small goldfish, 2 bumblebee gobies and 2 bristlenose catfish. One of the mollies are fine but the other seemed very stressed out initially. This morning he seemed better but wasn't 100%. When i got home this arvo, the poor molly was on the gravel breathing deeply but not fast, and kept "falling over" to each side. Then it tried swimming and got stuck in this spinning on the spot and couldnt stop, it was awful. Now its stuck upside down with its head and spine on the floor and it cant get up. Its almost as if it's top end is too heavy. I isolated him in a hospital tank but i don't think he will last. Could it be swim bladder disease? Is there anything to cure him? Thankyou for your help.

ANSWER: Sarah, I doubt its Swim Bladder. tHe fish would be able to swim but updside down, sideways, every way but upright. The fish is very I'll. Did you add some Sea Salt to the water? Mollies need a little salt becuse they live where the river meets the sea. be careful though because you other fish may not like the salt. the salty water could affect them badly though in that small amount is unlikely. A word of warning given.
  Exactly what the fish has I can't say. Check the temp, ammonia, PH. The one fish could just be stressed even though the rest took the change fine. Sorry I can't say exactly. If I had to bet on it I'd say the change from store to tank was too fast. Mollies need salt. Be careful when buying them. Can you other fish handle salt? Ask at you store.

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QUESTION: Unfortunatly he died this morning :( At the pet shop i was told they would be fine with my other fish and that they didnt need special requirements. I might see if i can swap the molly back for another fish because bristlenose don't like salt water, although the goldfish and gobies wont be affected by it. Thankyou very much for your advice :)

Answer
You had learning experience in economics. "sell it no matter what".  I do not mean to belittle certain businesses but PetSmart, Walmart are not in this fish business. Their employees often know very little about what they sell. I suggest since you are new to the hobby go to a tropical fish store. Ask them everything you can think of. They will know. A few fish suggestions for you: Angelica Catfish, silver dollars, hatchet fish, cardinals, Angelfish, guppies, gold severums, leporinus fasciotus, black shark, tricolor shark.