my recommendation is use your tap water, treat it for chlorine/chloramine and add some crushed coral to a small dedicated cannister filter. this will elevate your gH, kH and pH and accomplish everything your Malawi cichlids need for optimum health ... and will be a heck of a lot cheaper than RO water and all those other unneeded commercial chemical products.
"cleaner" in what regard? the absence of any mineral content? true, but fish cannot live in "pure" water and thus you need to purchase special additions such as a product called "RO Right" to add back those very minerals which the RO filter has removed. while your tap water 'may' have an insignificant level of ammonia, your biofilter should remove this without your need to do anything about it chemically.