I never saw how big your tank is, what type of food do you feed and what bio-load (Fish) in tank. I have an fx5 on 2 of my tanks and they get clear over night when I do a tank cleaning and filter change. Are you cleaning the sponges on fx. You might want to try a diatom filter if you want crystal clear water. I use mine all the time after a water change and my water gets very clear and no floaties in the water. I use it on all 5 of my currently set up tanks. As for your test parameters, they are fine, if you do a 40% weekly water change you will not see nitrates, all the rest are within parameters as you want them. If a fish is gasping, maybe it was stressed or do you have airstones in tank.