I've found those test kits to be hit or miss mostly miss.
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I can say I don't sell many of them. Smell and sometimes visuals with water not being as clear are usually our telling signs. For the rare occasion someone might want to try everything before replacing, it is an option. I do think the OP could try cleaning their ozone line just in case.
P.S....sorry for the funky quote, my phone is obnoxious.