I'm wondering if your filter isn't sufficient as Mandy suggested. In general, it is recommended to have enough filtration for double the size of your tank.
I doubt that's the problem, unless the OP cycled with his tank's full population of fish (in which case they would likely be dead or dying by now). With the small number of fish generally used for a fish-in cycle, his filtration should be sufficient. Personally I don't subscribe to the double filtration rule of thumb when talking about canisters. HOBs, sure, they probably need at least double filtration, but cannisters hold way more bio media. I still think that you should over filter even with canisters, but 110 on a 75 seems sufficient to me, even when the tank is fully populated.