It became old school for some reason, but when you read about water treatment and public aquariums, they all (for the most part) run ozone on a controller and or UV sterilization. “Both” have central filtration so they can’t risk contamination in one system to another, or even within the same tank. A "small" store owner told me he brings in 20,000 dollar’s worth of fish each month, they have a 8 foot skimmer in the basement running ozone and UV is design to run in line flow. Basically UV is cheap, its kills micro algae and ick, that’s it. Ozone is 500 dollars with controller, pricy, but it test ORP (redox potential) the ability of the water to handle waste. A reef is 325-390, so they test for 425 in the sump. For invertebrates they drop it to 325 because they filter feed. The commercial units are made by companies like Sanders in Germany. I used them, and Red Sea.
UV is cheap and for fresh and salt water (39 dollars at Petsmart), Ozone with a controler is only practical in salt water applications, but, sewage treatment has used it since the 1930's (nothing new), the salt water pet industry just made it practical to use on a tank, with a reactor or in the skimmer. The drinking water at the grocery store used RO and Ozonization also. Quite common.
The fast answer is the water using either will look crystal clear and common deseases such as ick will be cured rapidly, the parisites jump off the fish in 24 cycles, they get zapped. UV is designed to be very low flow, thats all you need. The alternative was to isolate new fish in a holding tank with medications for common deseases brought on by stressed fish, apparently being captured is just that, stressful.
