Most fish are very capable of adjusting to higher or lower pH. Most fish now days are bred on commercial farms, so they are used to anything but what their natural habitat is. I keep my freshwater tank at about 8.3 (That's what it is right out of the tap.) Of course I should be getting an RO filter soon, so that will help out too. I've kept oscars and jack dempseys in my alkaline water and they did great. Just acclimate them correctly and I'm sure you could keep some of the larger cichlids and things like that, no problem.