It's not about shade. Transpiration is what lowers temperatures.
Plants love gray water. That is what fish tank water is.Are you concerned at all that any detergents and such in the grey water might adversely effect your plants?
I use to use our fish waste water and the plants loved it. Our fish died and we haven't had the tank running for months.
I'm tempted to get some more fish just so I can have the water for the garden.
Our backyard has several trees and shrubs. due to some of the run off from our rock garden most of the grass hasn't gone brown in our back yard. It also helps keep our down stairs cool.