chubbyone: This particular type of rock (typically dubbed "Lace Rock") is usually used in marine setups and is usually harvested from marine environments. So it's always best to clean them well in boiling water and to let the soak for several days.
Each piece is different, really, since the critters that grew on them when they were submerged weren't always the same. Also depends on the amount and type of sediment that's caked on the rock, as it's quite porous.
Not worried about pH fluctuations because I've used this type of rock for years. If anything, it buffers my pH a bit. I also use substrates that lower/buffer pH for shrimp. Neocaridina heteropoda are hardy and I've never really worried much about parameters with them.
If you're concerned about it? Clean it really well. Boil it. Soak it for a week in a bucket. Ditch that water, clean it again, soak it for another week. Then test the water parameters. That'll let you know if there's anything to worry about.