Please fix my blue hibiscus!

I can't figure out why but my Alyogyne huegelii's leaves keep discoloring. For some reason, my camera captured the healthy green leaves as yellow but you can still see in the picture the orangey leaves, they also yellow but you can't tell from it.

It had a mealy bug infestation when I was overwintering so I treated twice with systematic and that burned most of the leaves off. It's come back pretty well, and it's been a while since then, but it doesn't grow a lot and there's the leaves discoloring and falling off.

I have it in full sun, let the soil dry out slightly and fertilize only once in a while for fear of making the situation worse.

Can some one pin point the problem and tell me what to do about it?

Mine is doing the same thing, so I hope someone responds with the answer. I wonder if it could be the heat?

You would think though that they would like the heat being from Australia though.

Is your's in the ground or a pot?

Mine too was having and losing yellow leaves,little epson salt helped her out a lot,all green now.
Mix a couple teaspoons around the base 5 gallon pot.

I just planted it in the ground today b/c things do better in there around here. Should I dig up and add a couple of spoons full?

Just sprinkle it around the base and work it into the soil a little, will be just fine.

Thanks, will do as soon as it stops raining, which it's been doing on and off. I love that I don't have to do it manually. The plants are really liking the humidity too.