Im not a soil expert like the guys above. But if your plant bounces back in the evening it might be because its hot and humid.
Can you get shade cloth in Thailand? Shade cloth comes in different grades to block part of the sun. Ive seen everything from 30-70% shade cloth (here in the states the % number refers to the percentage of sun blocked, so a lower number lets in more light).
You might try shade cloth over the plants, which will block part of the suns intense rays but still let them get filtered light, and also reduce temperature.
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