Aquarium Supplies World

I have a 150 gallon saltwater aquarium and want to convert it to freshwater. Can it be done and if so how do i clean it?

The water in my outdoor aquarium looks like someone poured a cup of fruit punch in it. It’s pink. I clean it change the water and everything, but eventually it starts to turn pink again. I have four goldfish in it.

I have an established freshwater aquarium. When I do water changes, I want to be frugal and use the water to water my plants. Is this a good idea?

The old aquarium water has nitrates and some nitrites and is Ph balanced. There is also some diluted salts in it.