The original post has been edited, but it said they had arrowanas, koi, goldfish, and tropicals. I took it to mean they were all in the same tank.....guess I misunderstood though.
Anyway, flourite is an excellent substrate for plants. Rinse it well beforehand to remove most of the sediment that will cloud the water. If you plan on adding it to an existing tank, it would cause some cloudiness when you add it. If you are setting up a tank, using a plate to break the water as you fill it will help to keep the sediment from getting stirred up. You will still see some cloudiness at first, but it should clear up within a day or two.