September heat wave. Keep your plants hydrated. Give them 8 glasses of water every day no matter how old they are or what size pot they are in. Now that doesn't make sense. Why do "they" recommend that for humans? Give them water before they are thirsty? It sounds like someone hired someone to prove it. And that is the problem with doing internet research.
"The root zone temperature is the Most important factor......" means that they sell a soil warming system. Try turning off the lights for a few days and see what happens. It took a long time to finally get some answers.
So, I found out from university research papers, and other sources that were purely science based, that the root zone temperature is a big deal. Not the only deal, but an important part of the puzzle.
My plants look very happy. One thing that I may have overlooked was that the rainwater I have been collecting should not be left in the hot sun. Now I collect it and store it in the cellar where it is cooler. I also added an air stone to the water tank (autopots). The pump draws 0.5W. I know that warm and stagnant water loses oxygen quickly. Fish hate it so I'm sure the plants do too.