You want to keep it as close as possible to their natural environment. I have my tang tank at mid 8. The water here is AZ is hard as a rock and they love it..
high and stable are two different things. Keep it stable, where are you getting the fish? Check to see what the ph is there, and keep about the same... key is stable...
for calvus it's obligatory to have a high ph an stability in the water casue these fish is very sensitive
if this fish don't count on high ph.. it can shock an die..simply as that.. eventhough you have a high ph and you change more water than recomended or usual..it can be shock to
of the tanganyika lake.. calvus is one of the more sensitive fish to water conditions.. but if kept right is one of the more beautifuls and intersiting ones