The pH in our area is about 7.8ish, and it's never been a problem for our rays. Just make sure you acclimate them extra slowly if they are coming from a source that has extremely lower pH, and keep the fluctuation to a minimum after they are acclimated as others have suggested - the inconsistency of pH if you are trying to do buffers/acid regulators while doing frequent water changes from the tap will be more stressful than just keeping it at the higher pH. Best of luck to you! They are very much worth the work 
