If it were me, I would do a few 50% changes every other day. After 6 months you probably have an obscene nitrate reading. lol
Juts be sure to temp match the water and match the salinity. I regularly do 50% changes with no ill effects.
Not only would it be a great idea to get those nitrates down for the shrimp but also for the anemone. I am shocked it has lasted this long.
But good luck, and get to those water changes! A 29g is eezy peezy to do a change on, try having to do changes on 180g, then I could see why you were slacking. lol But seriously, get them done, your tank will thank you.