hi, and welcome forum!
first of all, do you have a 6 fool 125 gallon tank for them? thats is the the minimom for a colony.
anything less than 6 feet you would only be able to keep a single frontosa
for frontosa you would need a ph of about 8.2-8.4(although anything in between 8.0 and 8.6 would be fine)
its best not to keep rocks like slate in the tank becuase when frontosa bolt they are so clumsy and will almost deffenitly knock over the rocks but hiding spots are needed.
anything other we would happly anser your questions in the african/oldworld cichlids forum:
http/www.fishforums.net/African-Old-Worl...chlids-f13.html