PH Buffer, Die Die must. Period. Options

[mountain]

splitted from thread here.
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I think for PH crash it might be misleading to have SODIUM BICARBONATE as 1st line of treatment .. SODIUM BICARBONATE is for buffering water, and not for treatment of fish's health plus if the PH crash, HB wouldn't advised you to dump 2 teaspoon of BS into the water immediately

[CP]

Hmm.. would the administrator help to split this buffering discussion into another topic.

Frankly,I have either not buffered my water before or have been doing it without realising.
I have not heard of buffering till recently.
After reading the threads I conclude that it meant stabilising the pH (in our case preventing the pH from dropping as goldfish prefer slighlt alkaline water) so that the fishes will not experience a sudden rise in pH during water change.
My pH has been quite stable ranging from 6.8 to 7.5 for the past year.80L per goldfish,3 feeds per day,80% water change per week.
I also understand that most bros use baking soda.I have corals and oyster shell in my filtration.My question is,are these "alkaline" items acting as a buffer (raising pH)?They were put in during my tank setup at the recommendation from my friend who keeps koi.(koi and goldfish same family).I noticed that oyster shells will dissolve in the water over time.So,can baking soda be substituted by these items?