At the very least, get test strips. They are not as accurate, but are better than nothing. My thoughts are, mbuna and discus have drastically different needs in PH and hardness. You may be getting fish that are domestically bred to tolerate local water conditions, but that is not guaranteed. Try asking about it before you buy them. My mother in law successfully keeps discus alive for about 6 months with our local ph7.4 and slightly hard tap water (she seems to think thats a long time, and doesn't mind buying new fish twice a year despite me trying to convince her otherwise.) I think she does about monthly 1 gallon WCs on her 37 with 4-6 discus :nilly: