Seachem Marine buffer and quick chang in ph

[garygb]

This morning I added 5 g of Seachem's Marine Buffer to my 50 gallon tank. Before adding it, I tested the ph and it was around 7.9. After adding the buffer, it measured around 8.3 The time between my first test (ph 7.9) and my second test (8.3) was less than 10 minutes. I followed the directions on the container, "add 5 g for each 20 gallons. Dissolve in atl least one cup of freshwater." I only added one teaspoon, 5 g, and I saw this dramatic change in ph. Is this to be expected, and is it safe? Is there a preferred way to add Seachem buffer?