Don't waste your money on the pond ones, they are not as good and garbage in my experience. You'll just waste your money, you need a high quality one designed for marine use and marine parasites. Lifegard aquatics have the size uv for the aquarium size and flow rates
LIFEGARD® Aquatics has been manufacturing UV Sterilizers since 1986 for various industries such as Aquatics, Aquaculture, Pool, Garden and Drinking Water. The original QL series from Lifegard was the only UV Sterilizer available in the US for many years for Aquarium industry and mainly used in...
lifegardaquatics.com
I've not lost any pod population. Pods life in the rocks, if they end up in the water column, they become fish food well before they end up in the sterilizer. Mind you I haven't ran mine now for 8 months and has been all good. But at the start of when adding new fish I would 100% recommend it if your not going to QT(I'd probably recommend even if you do QT). Also be patient and buy from a reputable store and if you can go see the fish in person, make sure they look healthy and they are eating. Fish can be hard to get eating if they don't eat in the store
I'd run it 24/7 the purpose is to kill off any parasites that spawn into the water column and reduce the numbers