I don't think I'm the one to be asking about calatheas because I don't think they like me!
My experience is yellow leaves and brown tips are the order of the day with these plants.
I minimize yellow leaves by keeping plant on dry side and simply use a scissors to trim away brown tips.
Normally brown tips are salts and other impurities being pushed out of the plant so technically, distilled water should be better - but tap water works just as good for me.
I would be stingy with nutrients to minimize salt build up I use and recommend Dyna-Gro "Grow" formula.
I leach plants with regular tap water every couple of months. Flushing the root system is important - a big benefit with hydroponics because it's impossible with soil.