for me, a pretty good estimate for glass tanks is 10# per gallon. that will usually give you a little margin for error without being way out of the ball park.
i use root tabs with my val, and swords. those are the only 2 i target with tabs, the rest just get liquid ferts. for me, they seem to like it, but ill admit im not always on top of adding liquid ferts.
i cant see an issue with sandiego's climate. temps dont tend to be extreme, and even the chill in the middle of the night is only for a couple hours. that wont drop your water temps too much.
you have another filter with established bacteria, you should be fine to remove and treat them. just dont over feed, as you will be removing some of your bacteria.