I think you may be looking at the numbers a little incorrectly. The FX6 is rated to turn water over around 900 gallons per hour. It is advertised to be adequate for up to a 400 gallon tank. Of course this number is generally believed to be without any media present in the canister so it is probably considerably less when working properly.
That being said and I am not an expert on your fish but your tanks water does not look healthy. It may just be the lighting but it looks cloudy. I think if you would like a better assessment of the situation you should give us all of the API test results especially nitrates. Those are two fish from what I have read here produce copious amounts of nitrates. Your Filtration does not take nitrates out of the tank.
That being said I have a 150 gallon tank and I run two Eheim 2217 and one FX6. I believe that equates to about 9x turnover of the water. Less considering the media.