I didn't take any chances and did my 2/3 water change on both the talapia and my goldfish because my ammonia levels were high in the goldfish pond and choosing to error on the safe side in the big tank. I also read that PH isn't a problem with talapia and that they anything between 6 and 9 is good and they can survive to a ph of 10.
Here is the link http://docs.google.com/viewer?a=v&q=cache:ngXcn24S-IUJ:www.aces.edu/dept/fisheries/education/ras/publications/species/283fsTilapia%2520life%2520history.pdf+ph+range+of+talapia&hl=en&gl=us&pid=bl&srcid=ADGEESj592TrfA0wsI9urfjJoo844IaS952fMXyf6ZqrbkjTzOxooB-9xO1HG3zxa83ZOJ995M85BUr9bztHFX1SMeVjvZJYKZrxrZW4qGQIyPi4CfbS6mhV7ABtJbgkfl1eG8R3EYYS&sig=AHIEtbSsoM37M2aNhVMS0EgQkma-Ew5R8w
