If it was just me (this is assuming I acclimated it to the tank lights properly, the results are true...etc) I would try a few things and see how the animal responds.
First I would double check my tests with a different brand/store...etc.
or
I would try a 40% or so water change. My thought process here is 0 NO3 and PO4 are possible for a 3 year old tank, but I would more expect you to have some values here, even if they are extremely low. Hard to really say as you basically gave us the bare bones minimum of information...As a result all we can do is easter egg the problem at this point and go from here.
If after a few days it didn't positively respond to the WC I would take a stab at slowly moving ALK closer to 7-9. I personally try to keep mine around 8, but all tanks are different so your mileage may vary.
Basically make small changes here and there for things that seem out of the norm and see where it gets me. Sorry, but with the little information you provided it's hard to give much more input then that.