Something like Miracle Gro soluble all purpose which has an analysis of 24-8-16 would do, I don't know what else would be available to you there. All purpose in the sense that it is suitable for container plants as well as in ground. In summer heat I would go easy on it though. Whether chemical or organic is personal preference but you may get better results from "chemical" in a pot. Organic fertilizers have to be converted to "chemicals" by microorganisms before the plants can use them so it partly depends on whether you have enough of the right microorganisms present in the medium. A "chemical" fertilizer that is all purpose would ideally have some of the nitrogen in a form that doesn't need conversion (nitrate). Maybe just try the MG at a quarter strength to start with and see if there is any improvement.
One thing to watch with watering is that if humidity is high it is easier to over-water even in hot weather. If humidity is low and/or it is windy they will need more water.
Plants that are deficient in potassium are more susceptible to environmental stresses.
