Black moor and rainbow shark in the same tank? That is asking for problems on a long term basis, thought you should know that. A black moor goldfish is a cold water fish and should have water temp range of 63 - 70 where the rainbow shark is tropical and should have temp ranges of 75 - 80. That is a huge range of difference and enough to make them incompatible.
Another reason for incompatibility issues is the nature of those 2 fish. Long term that would not be a good mix because the black moors don't swim real fast. With the aggressive nature of a mature rainbow shark, that leaves a black moor at a huge disadvantage both at feeding time and from being picked on.
I am looking at your signature... is this the tank you are speaking of? Neither a black moor or a rainbow shark should be in a 15 gallon tank, they both get way too large. A single black moor should have no less than 55 gallons, even if they start out small, because they grow so quickly and are such dirty fish. They have a very high waste output, need for higher oxygen levels (which is found in the cooler water), and they have messy eating habits. A full grown black more can reach over 6 inches in length and get as big around as a baseball. If you grab a baseball and look at your tank you will see its not practical, and these fish grow quickly.
In the case of the rainbow shark, they grow to 6 - 8 inches as adults, are known to be aggressive and territorial as they mature. Minimum tank size for an adult rainbow shark is 55 gallons due to their need for territory. As juveniles (if yours fits into 15 gallons it is surely a juvenile) they are a shoaling fish, which is likely why it is spending time with the black moor. This changes with time, and in a matter of months as that shark grows up, it becomes a solitary fish, known to fight with others of its own species and to wreak havoc on other fish that invade its territory, regardless of the size of the other fish.
I hate to say this but with your current population in this tank, the only fish suited for a 15 gallon from your list is the glo lite tetras. The glass cat will reach about 5 inches, and a 15 gallon tank is going to be an issue with space for that fish later as it grows up. Glass cats should have at least 30 - 40 gallons when they are full grown adult fish.
If you would like further help in sorting it out please let me know and I will do what I can to help guide you in the right direction. First and foremost the goldfish should be removed as soon as possible. If your lfs suggested to you that these fish were all compatible in a 15 gallon tank, that would be a good indication early on that they either don't know what they are doing or they are only out to take your money. Either way, their advice should not be trusted.