ok i have that same test kit , but i am not a big fan of them so much. as everything runs out i will be switching to the good stuff. the alk buffer that came with the test kit wont cut because you are supposed to add x amount of drops but only once a week or something like that. that wont change it enough in brackish water and will cause problems with fish health. this wont happen until the water gets down to close to 1.009, or even sits like that for a while. so i got the kent super buffer, which buffs pH and Alk. just add a Tspoon to some RO water and pour it in every day, as needed.
as for getting the water down, you just need to hone down a little system. i have a 29g, and i simultaneously drain 5g out and 5g back in RO, with vinyl airline tubing. sometimes morning and night i think to get it done in 48 hours. dropping 'fast' is ok, its raising salinity back up that should be done slowly. when the ick dissappears, count three weeks, and then bring it back up over a week. if you see signs again, then reset the 3 week timer.