Welcome to FishLore! It's great to have you with us! Here's a link on bala sharks right here on FishLore:
http://www.fishlore.com/Profiles-BalaShark.htm
I don't agree with the tank size on that profile. I think a bala should be in a tank larger than 40 gallons. And keep in mind that you should always plan your tanks by the adult size of your fish. It can be done with starting them out in a smaller tank, but you leave it up to chance when they get larger and you don't have the proper larger tank ready for them when they need it. Get the tank size you want first, and then plan accordingly as to what adult fish can live in that tank and thrive.
If you click above on "FishLore.com: Tropical Fish Information", you will see lots of other stuff on this site to help you get started. If you don't already know about the cycling process, please make sure you understand it, or you will not enjoy the hobby because your fish will stay sick or die on you. Here's a link for great beginner articles to help you out:
FishLore Article for Beginners
I'm assuming your tank is the 10 gallon tank, so if I'm wrong, please let me know. If I'm right, your tank is definately too small for the fish you have in there. They will produce way too much waste for that size tank, and you will never be able to get the water chemistry right. Black moors are goldfish and need at least 10 gallons each, so the bare minimum you would need for those 3 fish alone would be a 30 gallon tank. Some say goldfish should have 20 gallons for the first one, and add 10 gallons for each additional goldfish after that, making your minimum requirements a 40 gallon tank. Goldfish are very messy fish and produce a lot of waste. I agree with boxermom about the pleco also. If it's a common pleco (what you usually see in the fish stores just labeled as a small, medium, or large pleco), they get quite large, and really should be in around a 100 gallon tank. Mine is over a foot long.
I'm not trying to pick on you here, just letting you know what you are in for if they are in too small of a tank. Please post your water parameters (ammonia, nitrites, and nitrates), and we will be glad to help you with all your questions. We love talking fish here, and will get you guys all set up in your tanks. Once you get the basics down, you will love this hobby!