Im starting to dose the tank with 2 part.. When you do water changes do you buy salt that closely matches the levels in the dt or do you alter the levels of the water change water to match the dt? if the new mixed salt water is higher than the dt how do i lower it or if its 2 low how do i raise it. should i add 2 part to the new water?I have a 40gal tank mabe 50 or so gals with the sump. I have rowa phos running about 50grams..I add 20 ml of 2 part daily the cal stays 460-480 the alk is around 8.2 but sometimes dips to 7.8..I think it was because i added 15 ml for a few days instead of 20 but the cal didnt drop. I have about 20 frags mostly lps and zoas one sps..I am getting nice coraline .ph 8.2 steady... I want to get to the point where I can add more sps in the future.Im trying to learn not to cause any swings in alk by the things I am doing like water changes and adding 2 part..To me 20ml seems like a lot for a tank with only 20 frags.. do these corals suck up that much?All the corals are healthy and growing.I use reefcrystal salt roid water and test with salifert.The tank is fairly young at 50something days..If the sps take alot more out of the water mabe I should think of using a reactor for cal..Any body with a mixed tank that uses 2 part how much do you use?