To be successful, you don’t have to know anything about aquariums beforehand. Training is available online through aquariummaintenancebusiness.teachable.com. In fact, I would almost prefer that a person not know much about aquariums so I can properly train them to do it correctly from the beginning. There are so many methods, ideas and opinions out there in the hobby that may be fine for an aquarium at home, but doing this as a business is different. Businesses are about making a profit. How you design, setup and operate an aquarium is directly tied to your profitability. You need to know where the hobby ends and the business begins.
You need have good people skills and to be able to work with others. Your success is directly tied to your ability to effectively communicate to potential clients and to work with them to find & fulfill their needs.
Last is Motivation. Success is also directly linked to the level of work that you put into this (or any) business.