I would say poor drainage / overwatering. Hard to say which outdoors. Then leading to a nitrogen deficiency since lower leaves are yellow on left plant.
Feed light nitrogen and see if they darken.
can you not get cuttings or seeds from a fellow grower locally? I know they are really on top when it comes to checking for organic matter coming into Aus so that may be your issue. Legally you arent allowed to bring viable seeds into Aus as far as I'm aware.
wow, thats quite a high temp. I think I used to chill mine down to 18 degrees. Makes it harder for pathogens to develop and also the colder the water the more dissolved oxygen it can hold. Looking very good though buddy.