I use a product called Marine Buffer from seachem. Just follow the recommended dosage and you'll have no issues. Each time you make a water change, you'll need to add it again, but test your water first.
I'm sure this site sells a full line of ph buffers that will work just as well. (I always try to support these guys, since they created this incredible forum for everyone.)
Good luck and let me know if you run into any problems.