My fish tank stinksHelp me please

I got my new fish tank(75 gal) a month ago.I have 4 Koi fish and 3 fish which clean the glass.Few days ago water became cloudy(almost green) and now stinks badly.I need some advice.Help me please.

You have probably fed to much and your tank hasn't the ability to deal with the excess food. Change 25% of the water today and starve your fish for three days to avoid sickness from polluted water.

The stuff that lives on your rocks is essential in keeping your tank healthy. Beneficial bacteria digests fish waste (ammonia) and converts it into nitrites. Other bacteria converts nitrites into less harmful nitrates. This cycle tanks time to develop and until it does cloudy water, bad smells and sick fish can occur. Be a bit patient and it will develop. Feed a lot less food, and change 25% of the water weekly (use a gravel vacuum) and make sure the temp of the new water is the same as the tank. You don't want to destroy too many of the beneficial bacteria when you do a water change and changing too much water or having it at the wrong temp stresses them. Also, your filter media has a lot of the bacteria growing on it. Don't change it too often (and never at the same time as a water change). When it start becoming clogged, rinse it out in cool tap water. Only change it when rinsing no longer is effective.

I would also suggest adding some freshwater aquarium salt (one tablespoon for every 5 gallons). It will help avoid sickness in your tank.