I agree with Copperhead here. Also, it should tell you on the bag what kind of rock it is (and where it came from).
Just because it states "Safe for any aquarium" doesn't mean it is. Use the vinegar, if you are running a tank with higher PH required fish, depending on your water at home (Hardness) it could also be safe. IE if your water at home has a GH of 75 and your fish need a higher PH, this gravel will work well. However, if your GH (General Hardness) of the water you are using is 150 (Hard - 300 Very hard) you may want to reconsider the rock.
If you have already opened the bag, using a glass, put around an inch of gravel in the bottom and fill with the water you are using. Wait appx 1 hour and test the water tosee what your ph readings are. This should give you a good idea.
It is nice to know that someone realizes the type of gravel does play a role on the PH levels of your tank.
There are river gravels that look porus but are not. It is always best to check. Good luck.