I’m changing a 40 gallon tank to a 90 gallon tank for Discus only. There are 7 breeds I like, would I be able to have an adult pair of each in the tank with a few Neon Tetras, Black Widows and Cat fish (to keep the algea under control)? What is a good variety of plants to have in the tank and is it suitable to have drift wood and rocks in the tank as well?
You can have many adult fish in a tank but not 7 breeding pairs and breed in the same tank. Of course you can keep them in the main tank but they must spawn in a breeding tank. As long as they can get along well you can have other small fish in the tank. To get the algae away you have to control the light. Too much sunlight will encourage algae growth. Plants and drift wood are good.