Mexican Pot/Bowl Rock and PH in Planted Aquarium

[Tombeaux]

For those of you local in the Seattle area, the Indoor Sun Shoppe in Fremont has a huge pallet of what the owner called 'mexican bowl rock' for house plants or succulent planters. He said it was too hard to shape into bowls and was afraid of loosing money so I told him people might use them for an aquarium. He sold me them at $5 a rock which were about the size of a 2.5 to 10 gallon tank. 

I first dumped a sparkling water (ph about 3.5) and it fizzed after the co2 released. I then used lemon juice (ph 3ish) and that seemed to fizz less. I then used white distilled vinegar (ph 2.5ish) and that fizzed/hissed a bit less but still some. I have a 65 gallon tank and was planning on using just 1lb of crushed coral in the substrate of seachem red and fluval stratum. I also plan on having c02 and my tap is typically 6.4ish or less. So I have some uppers (coral, seachem alkaline/equilibrium) and downers (soft seattle water, stratum, and co2).

Has anyone used these rocks before? I am trying to discern if it will raise my ph?

[Chick-In-Of-TheSea]

This could help:

The rocks you posted look like lava rock to me.