You say "fish that require low p.h (6.5-7)." What fish are these? And do they require it for survival, or just for breeding?
The ideal range or recommended range of pH that you read in all the species descriptions is a TOTALLY different thing than the range the fish can live in comfortably.
My tap is 7.8. All my current fish prefer a neutral or acidic pH, according to the literature, and do great. It's stable and water changes are a breeze. Both the fish stores I go to regularly use city tap water just like me (dechlorinated) and it's what the fish are used to when I bring them home.
If your brother is a beginner the best advice I can give is NOT to play with pH. Beginners have enough problems without dumping more stuff in the tank thinking their pH needs to stay at 7. It makes everything more expensive, more of a hassle, tends to result in fluctuations which are harder on fish than a stable high pH, and is totally unnecessary in most cases where your tap water is drinkable.
If you could specify what particular species your brother has in mind, it would be easier to say what conditions they require.