Once or twice a month with your stock list is not sufficient .Pick a day do your water changes on that day of the week with consistency .Also how often do you feed cichlids are messy you may want to only feed every other day.
I agree 25percent once a month or so , isnt enough. At least 25percent a week. What I do is 30 percent and gravel vacuum on wednesday and friday another 20percent and touch up with gravel vaccum. Seems to work ok so far. I also lean toward heavy bio filtration and do not use carbon.