I have an fx4 as the only filter on a 100 gallon and I'm happy with it, no issues at all. So if you used both of those filters you should be good to go. Having said that, if your on a budget you could get by with a decent affordable air pump and two large sponge filters along with your current canister, until you can afford the bigger filter. Sponges are amazing for beneficial bacteria. They don't do mechanical filtration very well (your cascade would take care of that), and many people just don't like the look. But theres no denying how cheap and effective they are.
