Was that damage before the fert tablets or after, has it ben overhead watered?, Did the sun strike previously shaded leaves when you moved it.

How hot is it?

Hi miketree, it's hard to tell if it was indeed the fertilisers that caused the damage as we changed a few things at once.. We aren't overhead watering him, and often we don't water him more than once a week.

He was previously in full afternoon sun (average mid-high 20's Celcius) with no problems but we went on a holiday for 1 week and the weather was mid 30's so we left them in a shaded patch during this time.

I have tried to remove the fertilisers and placed him back in the sun but he is still not happy :( his trunk/roots have started to go kind of wrinkly too.

With that tiny amount of soil, I think you would have to be ultra careful putting fertilizer on. My guess you had a bit of fert burn, make sure you water enough so that any built up salts wash through the pot.