I just realised you were the same person with green water in the other thread. 6.6 from the tap will rise as the carbonic acid gasses off over night. For your ph to drop there is something wrong. I do a forty percent water change every week. I think you need more water changes and less food. Trust me the fish won't starve. I am sure they eat like horses, all cichlids do. It tricks you into thinking they are hungry. But remember what goes in must come out!. I will bet you if for the next week you don't turn the light on, add fresh carbon to your filter, feed once a day and do a twenty five percent water change everyday your green water will be gone. Then do a weekly forty percent and still only feed once. Your ph will stabilize and your green water will be gone. Try it, its one week, you aparently have been dealing with this almost a year.