It does not look like the AlgaeFix affected your cycle in any detrimental way as you have no NH3 or NO2. You must do some quite frequent and decent sized water changes to keep that NO3 that low
Since you mention this heightened aggression, I would bet that this fish is a female and is full of eggs and ready to spawn. Some fish will lay eggs even though there is no male in the tank.
I would just keep those water parameters as good as they already are and continue to monitor the fishes appearance/behavior...
Burt