Welcome to the group! I am new here too
If your pond is brand new, green water is typical. Does it get any shade or full sun? The more sun, the bigger pain the green water will be.
Our main pond is about 6500 gallons, with a 2500 gallon bog that is connected via a water fall (the bog sits about a foot higher than the pond). We are only running ONE filter right now (but have lots of plants). The way ours is set up (for now), the pump intake is located in the 6500 gallon area, and discharges via a Laguna Filter Falls 5000 into the bog, with an 8,000 gallon per hour pump that is split... The filter falls 5000 has 4 outlets at the "falls area"... 2 are set up as the "water fall" as the filter was designed for, but 2 of the others run into a pvc grid that is buried in gravel (with lots of holes in it) and another line from the pump is running the UV to another waterfall... We do NOT have enough filtration by any means! We are getting away with it as is, thanks to the plants... WHAT you need for filtration depends on exactly what you are running.
General rule of thumb (IMO) is if you are going to have fish to "stocking level", for an 8,000 gallon pond, you should be able to filter AT LEAST the 8,000 gallons per HOUR, but better is 16,000 gallons per hour. With the help of plants, you can "get away with" less.
With the way we OVER stock, we need to get more filtration on our pond, but have been holding off, as we are adding a lower pond next year (40 x 50 liner minimum) and our design needs are very different...
I also refuse to use any chemical in our pond, nor do we do water changes....
Hope this helps,
Geri