Keeping the troughs out of the daylight helps slow the algae growth, but if you want crystal clean troughs, you still need to scrub them out.
I was thinking that in the first place but still went with the bluing. Which, if I were going to use something, it would be the bluing. My horses really liked drinking the water at that old cowboy's ranch.
If you're horses are on your property to where you can control what kind of tanks you use, I would switch out the big tanks to 20 gallon muck tubs for the warmer weather.
During the summer I have 4 water stations and the only one with shade is the one under the overhang at the barn.
I have a total of five 20 gallon muck tubs that are out in the sun and the 150 gallon rubber tank is under the overhang.
Those muck tubs are much easier to handle and faster to clean; plus the horses drink them down faster so you're not wasting as much water when you do have to dump them.
In the winter I only have two heated stock tanks for the horses and they are both at the barn.
I use a fish net to clean the tanks and tubs every day because it extends the "life of the water". Unless we have a dry winter and get a lot of wind blowing dust/debris around, I only have to empty the stock tanks once in the winter to clean them and then again when spring gets here and they are getting put up.
It goes without saying that one has an extended day doing all of this rigamarole. I do work but am old enough that there aren't children at home to also take care.
I am sorry to say this but I using fish in the water tanks is not my idea of keeping them clean. They have to do their own business somewhere and that is in the water tank. Plus I have one horse that would swallow those fish "just because". He is 15 and still can't keep anything out of his mouth including the cat, paper towels, and plastic bags. I can't leave anything in front of him for two seconds and the bobtail cat he likes has learned to keep it's distance from him - even though Rusty does pick him up by the scruff of his neck