my second loss

[medic_eva]

i did two water changes, one 20% on monday and one 10% one on tuesday after i found my shrimp dead. i dug up the old posts on reef chemistry, but i cam a little worried about adding any baking soda to my tank, first because i can't tell what my pH is due to a crappy tester, and because i would have no idea how much vineger to add to make sure the pH doesn't get higher. has anyone ever actually put baking soda in their tanks? i've read that for every 50g you use 2 teaspoons of baking soda. but i'm worried about doing that without knowing my pH level. i'm using a hegan kit and it comes up as a grey blue color and doesn't even come close to matching any color on the list.

any ideas?
eva