Hi and welcome to AA!! I am afraid I am going to the bearer of bad news. Your local pet store has been giving you some awful advice. 46l is only about 12 gallons. Black moors need a minimum of 20gals for the first fish, 10gals for each fish after. Moors and plecos are not compatible. Black moors are a species of fancy goldfish. They are not compatible with tropical species either because they have different needs for housing, diet & temperature. Your going need to address your stocking issues as soon as possible in order to have happy, healthy fish. This will mean either investing in another tank or returning/rehoming some fish. Please take the time to research the fish you are interested in keeping PRIOR to purchase in order to be assured you will be able to adequately house, feed & care for them in addition to their compatibilty with each other. Please dont hesitate to ask questions because we are here to help!!! Heres the guide to setting up a
fw aquarium- it has links to both fish-in & fishless cycling:
Guide to Starting a Freshwater Aquarium