After reading this, I'm almost 100% sure your tank is not cycled.
You should read up on the stickies here about tank cycling. It's very important and I would not put any fish in a tank that isn't properly cycled or started with well-seasoned media.
I agree but if he's getting 0ppm readings its possible all the water changes did cycle it or help atleast.
Op hold out on moving the cat for another week or two and keep checking your parameters for another week or so if you have a spike in any readings hold out as long as possible.
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