have you got a water report to check to see if you have nitrates in it? its very likely you have, at one point my tap water had 30ppm NO3 in it before it even hit that tank.

As far as CO2 is concerned, make sure your not adding it at night, and that you have good surface movement 24/7.. thats extremely important. Gasping fish isnt caused by CO2, its caused by lack of O2.. adding CO2 wont deminish O2 but it will lower the fishes tollerences to it.

For dosing, follow the link in my sig for the nutrient calc, that way you can dose for the correct size tank, but if your adding tap water, get a water report to check whats going in and adjust your dosing accordingly.

I would get hold of some Tropica Nutrition for your traces, add that on the EI off days and youll be all set id say. Fish arent going to produce anything you want really other than Nitrates via nitrification and even then, not enough of that either. With you tank flourishing, youll be amazed at just how much the biomass will absorb.