Temperatur light Height etc...

31 degrees celcius is pretty hot for weed, but it should still be able to grow, although the heat may stress out the plant a little.

Today was a hot summer day might have been that ... ive got the light 45cm away from the plant is that right ? How can i add more co2 a normal fan will do it ? Thanks guys

I can't see if your leaves are showing any light damage, but the internode space looks fine. if the plant is growing vigorously, doens't stall for unknown reasons, no burn on leaves near top that worsens very quickly, or nodes stacke don top of each other, it's fine. All of these things happen slowly over time if you apply too much light. So, just watch that spacing between the nodes... make sure there is some space, but keep it tight. I like 1" or so and that tends to produce a good solid bud later on when i am good about keeping that true.

Hi! That is little bit too much unless you can add more CO2 to 1500PPM. The plants might handle it but they are not in optimal environment cos optimum is 25°C if normal CO2 levels in the tent