My tap water has a naturally high pH and hard water. A month or two ago my pH was testing 8.0 and my plecos are doing fine. I did notice last week when testing the tanks' pH it was slightly lower, maybe 7.8.
I tested the tap water again after that and got a similar reading. Not really sure why it changed, maybe the city was doing something to the water.../shrug
Not sure if its a great idea to keep it in a tank where the pH is intentionally kept high (for the african cichlids). I try not to mix African and South American fish, but thats mostly personal preference.