Baking soda is perfectly fine for raising your alk
(it will also slightly lower your pH). You should test your alk
the same time every day. pH has a slight affect on alk
, so if you test one day in the AM when your pH will be typically lower, you will get a different reading than if you test it mid afternoon when the pH is up.
FYI, if your tank is using alot of alk
, it is also using alot of ca
and mag. All 3 are used up proportionally. You can save some $ and make your own alk
and mag supplements. I've been doing this for years. http://reefkeeping.com/issues/2006-02/rhf/index.php