I HATE KENT. Ask James down at ET about our experience w/it. 0.2dKH and they are all liars and I'll leave it at that. Switched to Tropic Marin Pro Reef salt for over a year, but always had some algae issues w/phosphates. I used Oceanic, too high in calcium!!!! It measured 650 once so I quit using it. Instant Ocean was always way to low for my reef, around 325-350 and I always hated trying to rebuffer it and get calcium and dkh where it should be, but its good for a fish only tank I'd say. 3mts ago switched to Seachem Reef Salt and love it. No more phosphates, algae went away, dKh usuallys tests around 10-12, calcium around 400-420. It takes a little while longer to clear while it mixes, but it's not that big of a deal IMO. Also, I have found that Seachem makes a good calcium & dKh test kit, and I'm sure it works better together since it's all the same company and I like using the same company as much as possible. But, that's my opinion, and as always, stay away from Kent!!!!!!
BTW, I always used to do 40-50gal water changes a week, sounds crazy!!! I have learned over the past few months, that if I do 15gal per week in my 180gal reef, it seems to be a lot more stable. I always thought you couldn't go wrong w/big changes but have found my reef to be better since all the chemicals don't drastically change and reduced, then re-dosed. So smaller changes have worked better for me as well.