That tends to happen unfortunately when you go to a pet store, either A) they sell you species they KNOW are incompatible to make a quick sale or B) they themselves are really clueless about the fish.
Do all the other fish have ich, or just the pictus? Unfortunately, pictus catfish are VERY prone to ich, they seem to be "ich magnets" in my opinion.
What ich medicine are you using right now? Pictus are scaleless so you have to use certain medicines when treating them, or at least use at half dose, and you can bet your money on it that the freshwater flounder, freshwater dolphin are sensitive to medicines, along with pretty much all your other fish excluding the platies and mollies.
Right now though, if the sturgeon is a TRUE sturgeon, (you never said if it was or not), you need to return it to your pet store first thing in the morning, hopefully it won't get ich. If not, please post a picture or a description or what the name tag said or what the employees said, anything to help us identify what it is.
Saying it is a true sturgeon and you return him, this would be your remaining stock/stock needs:
-Freshwater moray eel (assuming you have
Gymnothorax tile not another species- high brackish/full marine, SG (specific gravity) of at least 1.010, temp ~80F, completely covered aquarium, sand substrate, eats frozen sea food, crustaceans, live brackish/marine fish sometimes, nocturnal, recommended tank size varies I've read from 30 gallons- 150 gallons, species only tank recommended, need lots of places to hide, maximum length 24" is
http://www.wetwebmedia.com/fwsubwebindex/fwmorayart.htm http://homepage.mac.com/nmonks/Projects/FAQ/4f.html )
-Bala sharks (ph 5.7-7.9, dH 5-15, temp 72-84F, recommended in groups of 5+ as they are a schooling fish, 125 gallon minimum size, omnivores- flakes, pellets, frozen, live, need vegetable matter, maximum size 10-14", see
http://www.balashark.info/bala_shark_care.php )
-Green spotted puffer ( max size ~6-7", brackish/or could do full marine even, need a diet of hard shelled food to keep their fast growing teeth down, species tank recommended, several feedings per day recommended, 30 gallon min tank size see
http://animal-world.com/encyclo/fresh/Puffers/GreenSpottedPuffer.php )
-Pictus catfish (pref sand or small grained round smooth gravel substrate, max size either around ~5" or ~10" depending on whether peruvian or columbian origin {Colombian Pictus Catfish: The small spots form almost linear rows along its flanks and its caudal fin is striped. Their semi-aggressive/ territorial behavior is focused only toward their Peruvian counterparts. Other than the occasional wrestling matches, they are quite sedate preferring to stay motionless in a favorite spot.
Peruvian Pictus Catfish: The large blotches are more random and continue on its caudal fin. Their behavior seems just as random, constantly swimming over and under the same areas for hours."" http://aquaticpassion.animal-world.com/index.php?showtopic=1788}, best in groups of 4-5+, min tank size ~100 gallons preferably a 5ft+ tank though, 75-81F temp, 7-7.5 pH, omnivore, see
http://www.aquariumdomain.com/viewSpeciesFreshwater.php?id=38
-Freshwater flounder (max size ~8", there's a variety of them, some truly freshwater, some brackish, hard fish to keep, carnivores that prefer live foods and are slow eaters, nocturnal, minimum tan size 55 gallons, sand substrate, low light, temp 74-82F, pH 7-8, 7-10 dH, will eat tank mates that can fit in their mouth see
http://animal-world.com/encyclo/fresh/miscellaneous/Tonguefish.php )
So as for stocking, you could probably do-
~150 gallon
-2 Bala sharks (get 3 more)
-2 Pictus catfish (get 2-3 more pictus)
-1 Freshwater dolphin (I'm assuming this would be okay to have with the pictus and balas, not 100% sure though)
For the 55 gallon, I'd recommend doing a species tank. So choose either the green spotted puffer, "freshwater" moray eel, OR the freshwater flounder, and return the rest, along with the sturgeon. Keep in mind none of these species are beginner friendly really and don't do well in newly set up tanks, esp not the freshwater flounder. You could try to do both the moray and the GSP in the 55 gallon (high end brackish or full marine), although GSP are very nippy and there is a chance of the eel trying to eat it, and them both dieing.
As for the platies and mollies, in either tank, they would become food probably for the other fish. So either make the 55 gallon a molly and platy tank if you want them to live as your other fish grow, or if you don't mind them getting picked off, then you could do the platies in the 150 gallon, and the mollies in either the 150 gallon fresh or the 55 gallon brackish.
Hope this helps!