If the alk
level is between 2-3 mEq/l, then your pH issue will not be chemical. Environmental causes are your main problems. If you do anykind of regular water changes (weekly?), your chemistry can still be off but most likely not the cause unless very high or very low. Adding buffers to correct pH issues is the wrong way to go about it unless your outside NSW
When you get the test kits, please post the numbers for the tank as well as your saltmix. Also give a rundown on how the tank is set up as this will have more to do with it than anything.
Be sure when testing pH it is done relatively the same time each day to guage stability. pH fluctuates throughout the day being at it's lowest point in the early AM and climbing throughtout the length of the photoperiod. Testing at the same time each time a reading is taken will give you a more accurate means of reporting.
What time of day are you testing the pH?