I don't know nu-clear canisters at all, but I can tell you what I have for reference. I have a pair of ocean clear canisters running with a Reeflo Dart at 3200gph. This is on a 180g tank with a colony of 20 juvie Fronts. It appears to be flawless and runs great (trying to be careful wording this as I really don't want to jinx it). My params are low to normal.
I assume that your initial choice of 1000gph with a single canister would be on the poor end of filtration for a 300g tank even with mild stocking.