You can use either one for PH control. I put in a link to a new product but I haven't heard any input on this maybe some others on the forum know more about this.

Here is a link that might be useful: C02 injection

CO2 has be used for years.

My understanding from reading several sources from the University of Florida, etc the safest/best type of acid (for the plant!) is sulphuric acid.

The method I use to make handling sulphuric acid safer is I bought a new 5 gallon fuel container from a hardware store, it's different color than my regular fuel can and I labeled it conspicuously so I wouldn't use it in my lawn mower, and I filled it with about 4.5 gallons of water. I then carefully (taking various safety precautions) transfer two quarts of 33% sulphuric acid which I acquire at an autoparts store. This diluted solution is relatively safe to handle with only basic precautions. I then use it to reduce the pH of my tap water to about 5.2