Water chemistry

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I am new to the salt hobby and I have a 150g reef aquarium, my current chemistry is:
Calcium 420
Magnesium 1170
Salinity 1.024
pH 7.98
Alkalinity 15.4

I was told by a lfs I had to raise my ph, so they told me to add seachem buffer. Which I did with water top offs and tank changes, and my ph stayed between 8.1 -8.3. But a friend said I should check my other levels and everything had dropped, cal 400, mag 1155 and my alk was through the roof 16 +. So I've stopped adding buffer and just add some calcium and mag, but my alk isn't coming down. Is this a problem? How do you get alk down? Should I be worried? Thanks for your help/advice.