calcium question

[fresh]

Hi all,

I have a 77 gal with softies and LPS. The lps being: hammer, candy-cane, and frog-spawn.

Do I really have to worry about calcium if I plan on doing arount 20% water change every 4 weeks?

Also do I have to worry about supplementing with anything else?

I have owned a 10gal nano for 2 years, and that one went very nicely but the reason is I did a water change every week, and I really don't want to do that with my 77 gal!!!

thanks

fresh.