so i plucked him out his pot this evening and low and behold, I found the problem, just as expected he needs a much bigger pot! ...
several arguments later with my husband on how i should be doing it, it's done and not a bad job if i do say so myself! It was so badly overgrown I think I might need to go another size up very soon. the 15cm was all I had so will make do for now. Thanks again for all the advice. I'm sure this will be the first of many!!