The best water for keeping tropical fish is the most stable water possible. if you tap water gives you pH 7.4 after aging, be grateful and do any water modification you do not have to do. The tigers will be fine.
My tap water is pH ~7.8, and I usually have a species tank of Tiger Barbs around- those, like Rainbows are hyperkinetec tanks. They live long and heathy lives lives without water mods.