I have read that you should do that... but I didn't. I really didn't do anything other than care for them, feed them, etc. The male will get more colorful when they are spawning. It is a noticeable difference. You will also see them kinda dancin' around each other, chasing, biting, etc. That behavior went on for several days before they retired. However, if they are already hiding in a cave and guarding it then maybe they have already spawned (how long have you had them?).
As for pH I don't measure pH really so I can't tell you what mine is... the reason I don't test for it is that I am not goign to do anything to alter the pH and it is one less thing to worry about. The fish, or most fish, will get used to pH levels provided that they remain stable. That is just my approach and it never hurts to check. I just don't like using a bunch of chemicals.