Determine if your market can support this business. There needs to be enough businesses or individuals in the area who could use your services. Someone living in a rural community might have a hard time finding enough business.
How much competition is already in the area? There’s a couple of other maintenance companies in my town but there’s enough business for everyone. I always suggest trying to create new accounts instead of taking them from other maintenance companies.
Talk to your local pet store to see if there is a need for aquarium maintenance and if they are willing to work with you.
After doing your homework, then you can put your business structure in place, purchase basic cleaning equipment then start marketing to potential customers.