Heat burn??? PICS

This is my first grow and my goal is not to yield, but instead learn the art. I am currently 10 days from seed and started seeing my first problem just now. I think i have heat stress or nute burn. Im using MG organic (yes i know but i have seen mixed reviews)...My temps usually get as high as 85-90 for some time throught the day maybe in 8 hour stretches. The cotyledons where turning yellow a few days ago and the leaves of the plant have always been a lighter green color the tips even more so. Long story short the temp was over 100 for 10 hours with 20 humidity then the tips turned brown and look like this. Im guesing this is heat stress.... take a look and help a brotha out

They havent gotten nutes so is this what heat stress looks like?

Def. too hot. What kind of light are you using?

CFL the box got closed without me knowing and the temp shot up

had similar problem . 85 and up with only 20% RH will do that . I'm using a humidifier to raise RH and have a PC fan blowing inside the box to move air around and over the plant.

For plants, the relationship between temperature, humidity, and CO2 are closely related. As you raise heat, you will need more humidity and CO2, as you raise humidity, you will need more CO2 and heat, as you raise CO2 you will need more heat and humidity. Having a high heat without CO2 supplementation (over 80F) with a combination of a low humidity (<50%RH) you are going to see major problems with your plant. Make sure you fix these fasts or problems will snowball! Young plants are especially delicate to their environment. Aim for 75F and 50%-75% humidity. People tend to neglect humidity. Humidity is VERY important to the overall health of a plant. Ballpark humidity should be as follows, Seedlings/Clones ~90% RH (Relative Humidity), Vegetative ~50-75% RH, Early Flowering ~40-50% RH, Late Flowering <40% RH. Also remember that with high temperatures your plants are going to release water through their leaves faster in an attempt to cool off, so they will drink water much faster, and also your medium will dry out faster so make sure to keep an eye on that as well.

Hope this helps, and goodluck!