30% is way too low! 50% every week is the best for a malawi tank standard!
at the start of your post you say you have been doing lots of reading i would worry what you have been reading i think if you improve you water reigeme your fish will benifit!
I completely agree with rifty, 30% is wayyyyy too little an amount to be changing for a setup such as the malawi/mbuna. A minimum of 50% a week is regarded as 'normal and necessary' and extremely beneficial for these types of fish, over filtration is always good too.
Although I applaud you for doing homework and reading about the setup and maintenance, you`ll find that other peoples personal experiences will be much better for you to take notice of
I have a 380L setup that has a sump system running underneath it, I think the amount of filtration that the tank gets is approx 4 times of what I would get from a Fluval FX5 AND I do 50% water change once a week, sometimes I`ll do 2 changes a week.
Your fish would thrive, their colours would improve even further and they are more likely to breed if the water is kept in tip top condition and that can only be good for your fish and the display you get from them