Thanks everyone for the tips. I have got some useful advice. I definitely need to increase my watering. I think that will help a lot. I find it interesting that people are growing them well at 37oC and above. My glasshouse can regularly get to 35oC and above during summer. I was concerned that was too hot, but obviously I shouldn't be.
I like the idea of the Nutricote and thought I would experiment with it, but it doesn't appear to be for sale here in Australia (other than in 25 kg bags for $180). It did use to come in 500g containers but apparently no more. There are other slow release fertilisers such as osmocote but I have read unlike Nutricote, at really warm temperatures osmocote will release all of its fertiliser at once and hence burn the roots. In a warm glasshouse during summer, this would happen often.