To be quite honest, if what you have are Tiger Oscars you are going to have problems really soon, since normally people would recommend at least 50 - 75 gallons PER FISH... so if you have 6 in a 50G you will more than likely soon end up with aggravation issues as they get older...
As for filtration, i would strongly suggest to aim for no less than 4X turnover, so if your running a 50Gallon tank, you want 200G+ turnover every our... i personally have a 200G tank and am running it at 4X turnover, and still want more... since as most people will tell you, you can NEVER have too much filtration...
In fact, i know a lot of people who do 12X turnover on larger tanks which are overstocked to help keep Nitrates, Nitrites, and Ammonia levels as low as possible...
Lastly, not to sound like a smart ***, but just cause you water is crystal clear doesn't always mean your water is fine, if your really serious about it, get a liquid test kit by API that tests those 3 parameters i mentioned above as well as PH... since these are all things that could come in very handy if you ever find yourself with sick fish in the future...