Any ideas?

hi, this looks like a typical K deficiancy. this comes normaly from a high PH problem, that locks out certain nutes... flush the medium with a lower PH,and a mild but complete NPK solution. afterwards adding only water for a few days. it will take 5 days for problem to start disappearing so dont play around too much. after 4-5 days start adding a stronger and complete solution. should help. not a big problem to fix, but must be corrected now or it will get alot worse...

thanks very much.

Heres hows she's looking now. Getting quite big (16 1/2 in tall) and nice and healthy looking, apart from some old damage and a bit of a shading problem towards the bottom.