Try to keep all of your tanks at the same pH and temperature so that you can easily move a fish without having to re-condition the tank in an emergency situation.
A pH of 7.6 - 9.0 is fine for Tropheus. It is important to keep it constant and not move a fish to a tank with a radically different pH.
Water hardness is not crucial to proper Tropheus keeping. As long as your water is moderately hard to rock hard your fish will do just fine.
I use four gallon buckets to do water changes, which generally are about 30-40% every week (or two if I'm feeling lazy, but really it is important to keep a good schedule).
To Each Bucket I Add:
© Copyright 2001 Teale Miller, all rights reserved
Miller, Teale. (February 01, 2001). "Water chemistry". Cichlid Room Companion. Retrieved on January 16, 2019, from: https://www.cichlidae.com/section.php?id=70.