I bought a little Fukien Tea from Walmart and the poor thing's leaves are turning yellow and falling off! I changed the soil with a bonsai substrate from Amazon but I think it's mostly for cacti. I've tried looking up what NPK value to use and I found something a while ago but can't remember the number.

Please do not respond with fertilization care or watering tips as I am already a bit angry with the internet and its lack of knowledge. The great Google overlords have failed me. LOL.

So what NPK ration do I need for a Fukien Tea bonsai tree? I think it's 6-3-6 but I can't remember.

Thanks

It really does not matter. Just use any general purpose fertilizer.

While discussing NPK levels for Walmart mallsai is a bit weird: fertilization is rarely the reason - and in most cases certainly not the cure - for plants that are yellowing. Better to review your watering regime. Look it up (tree species guidelines, top of the page)

How long have you kept the tree now?

Keep in mind that trees are slow adjusting. So if you change something, you need to take several weeks of not changing things so you can tell whether that fixed it. And instead of doing a dozen things just to try something, better just ask first.

In this case, you repotted. Leave the tree alone. Do show some pictures.