Everyone says water changes should cover most things until you get blah blah, and no need to dose with no corals, but no one can tell you anything correctly but your test kit.
I just set up a 20g with a couple of rocks and sand and the first week with no lights it dropped withing .5dkh...in goes a little soda ash to brig it where I want it, 8-8.5dkh..
So it is totally possible for your target ranges to drop on you even with water changes and no "corals" .you check and adjust accordingly to where you want you #s.
Test test test some people get by at doing just water changes but maybe their water changes change their #s and makes everything elevated then by the time they test it lowers to what they like but mean time its gone up and back down.
Water changes are not expensive unless your doing them for no reason. I change when phosphates and nitrates tell me to, and add the appropriate part A or B when alk, cal, mag tell me to.
Again thats basically my ideals on it but you gotta test for yourself. I use to hate testing until I wrapped my mind around how important it is, how can you add anything without knowing the current values? Get quality test kits, easy to use makes it not so daunting. Keep a log for a month or few then you will start to see whats going on.
Again only my 2 cents, its not worth much