I have 6 Koit fishes in a 300 gallon tank that is 3 weeks old). The water is not clear at all and I have a mechanical fountain filter-------what can do to clear the water. HELP ME PLEASE!!

You can get products to help clear the water. Check at your local pet store. They are drops you put in the tankl and they bind all the molecules together and help them either get trapped in the filter, or settle on the bottom of the tank.

You should also change the water regularly to try and get the old water out. 25% water changes every 3-4 days should do the trick.

Sounds like it's still cycling.