Down Under Disease?

[Antipodean]

Hello, fellow antipodean, i think you have a number of nutrient deficiencies going on which can be caused by either under fertilising or overwatering/poor drainage.

It appears the advice you have gotten is crazy wrong....eggshells and banana skins in container growing is downright wrong! i wouldn't listen to them.

they've/you've over-complicated it.....lets start from the beginning:

Your containers of choice should be a minimum of 30 litres, even bigger is better, make sure they have drainage holes;
Use just potting mix to fill them....no compost, egg shells etc. Potting mix is formulated to have the right amount of water retention and drainage and also won't breakdown so that balance is maintained. Compost etc will alter the balance and it breaks down quickly and affects drainage (waterlogging);
Organic fertilisers don't work in containers. They require microorganisms to work and potting mix is virtually a dead medium;
Use a soluble or liquid 'chemical' all purpose fertiliser (look for 'Flower and Fruit' fertilisers) with all the micronutrients (Fe, C, Mg etc). Fertilise at half strength once a week;
Your growing medium looks water logged, i think you are over-watering or have drainage issues. Stick your finger into the mix and if its damp don't water. Even better buy a moisture meter from Bunnings (about $10);
I don't think you have any major disease problems, maybe some fungal ones. Its best to spray once a week as a preventative. You can make a good one from baking soda, vegetable oil an water (google the recipe).

Good luck!!