It's really too bad using diatom filters fell out of favor. I've had tanks that just seemed "off" and running a diatom filter with just diatom powder or diatom powder and powdered GAC really perked things up. After reading what's happening with microbiomes and shedding of aging biofilms and mucus layers it seems reasonable things can get skewed to unfavorable species floating around. Running a diatom filter seems a particularly good way to reset everything as it's not selective like skimmers and lets corals promote what they want.