Substrate and pH question

[Vampire fish]

Everyone says for salt tanks you need a specific substrate because it will keep the pH where you want it (crushed coral etc.). But if salt water or adding marine salt into the water raises the pH anyway whats the issue? I want to use pea gravel from home depot that I'v always used on my freshwater tanks.
I learned that calcium and other things in the substrate is healthy for the tank. The gravel would not have this, I see now, but that would mean it is possible for me to gather lots of shells from the beach and put them into the tank no?
I realize this wouldnt be the most ideal setup for the majority of you guys, but it would work wouldnt it? A bunch of crushed shells ontop of some gravel?

 

[dallen2233]

I run silicate based sand in mine and I have no issues. All my parameters are steady. The salt mix I use has calcium and trace minerals in it so when I do a water change it adds it to the tank.

 

[Oddball]

Calcium is absorbed by organisms in a marine environment. Using crushed coral and/or aragonite helps maintain good calcium levels throughout the system and an even pH. Sand is fine in a FO setup but, it's importance increases with an increase in LR organisms, corals, and other inverts.

 

[Vampire fish]

Thank you I think those were great replies

 

[Wailua Boy]

I think by using crushed coral/live rock it acts as a buffer, otherwise you will see ph fluctuations over time