Cebu blue yellowed suddenly – are these roots bound?

Under a grow light that it had always been under, but it’s been getting a few less hours because some of the plants next to it needed less light. It’s on the same inconsistent watering schedule that it has always been on (but I always catch it before it goes wilts, and it has never complained). It’s been growing happily. The leaves that have yellowed are the first ones on every stem – I know that some yellowing is normal but I feel like they don’t just coincidentally yellow all at the same time..

I watered last night with tap water as per usual and it seems like it got worse since then. I thoroughly searched for pests. And no root rot. Is it just root bound? And what can I do if I don’t really have the capacity to size up the pot?