While freshwater fish have a low carbon footprint, tropical fish have a higher one due to the need of heaters and pumps. Try to look for options that are energy efficient.
Water also needs to be changed due to overfeeding and a build up of algae and ammonia. Try to only feed your fish the right amount. You can also search online for plants that reduce ammonia levels and fish that consume algae. This way you can change the water less often!
Finally, when you do change the water, use it to water your plants. It’s full of nutrients!