I've grown other plants in this spot on the balcony, in this same container with a similar potting soil mix and fertilizers: watermelons, pumpkins, tomatoes... but I've never had one die a death quite like the one this plant is going through. The yellow leaves at the base of the plant, that have been yellow since mid June are finally turning brown and dying off completely. The plant stopped growing a little while ago. The one melon on the plant is not quite 6 inches in diameter and just turning yellow now. Golden Midget watermelons are suppose to turn yellow as they ripen but this one could be turning because the plant is dying. The melon probably needs another month to ripen. But with all the leaves dying I don't think there's much chance of that.
The one nice thing about all this is that the yellow leaves add a bit of colour to the balcony.