An aquarium or pond organization should have a consitution and bylaws. These important documents formally set forth the name of the organization, its purpose, types and number of elected officers and voting procedures.
At one of your first meetings, you should review the proposed constitution and vote to accept it. Next, you should have your first vote for elected officers. It's a good idea to have all of the members sign a printed original copy of your first constitution.
The following document is a suggested starting point. Depending on the needs of your society, you may need to make changes.