ok first. unless you have some form of bad bacterial problem. do not remove gravel. even when moving tanks long distnaces to wehre a tank has to be broken down completely, I keep the gravel under water with air stones to keep good bacteria alive.
Is the water cloudy green, or cloudy white, or perhaps, cloudy brown?
if it is cloudy green, look at tank placement, is it in direct sunlight is the main thing? perhaps you have to much artificial lighting on the tank? Green water is an algae bloom. two main ways to get rid of it. either black the tank out for a few weeks I mean NO LIGHT touches the tank. do water changes at night, with as fewlights on as possible etc etc, use a few thinck sheets, or a comfoter or somethingto cover the tank.
ifit is cloudy white, it is a bacteria bloom. let it sit, but cut back on how much you are feeding the tank. If it doesnt go away, try getting something like a freshwater clam, or some other type of filter feeder. bamboo shrimp would be good, but I am sure the oscars would kill it.
The brown only applies if you have real wood in the tank, that is caused by tannins leeching out of the wood. it is actually a good thing as far as the oscars, or angelfish would be concerned. the situation is called black water, it is very soft but acidic, very difficult for bacteria to live in that enviroment, it eases the stress on most south american fish alot, and helps to prevent diseases. I have my 29 gallon tank under this condition, You can see colors in my angels that you have enver seen before they look so happy now that I did this
Anyways, keep us updated
BTW do not do water changed over 50% unless something is seriously wrong as well i.e avoid extremes in anything. even if water params are out of whack dont do a large water change to fix them. do it gradually. say droping pH by a point every few days if that is a problem. etc etc.
Good Luck
