First grow need help

The leaves are yellowing and you can see the bottoms ones are dying.
I see also heat stress but i don't know why the leaves are turning yellow.. maybe nitrogen deficiency or ph issue, which is it?

The first two leaves,Cotyledon, will die off. Don't worry they look fine.

New parent worry's syndrome...relax

You don't have heat stress! People say this but they don't understand the plant cycle and photosynthesis. Plants grow in hot weather as well as optimum temps; 70-75 would be considered glorious temps for weed but sometimes that isn't the case. Regardless of what folk say the plant life cycle is what is important here. If heat levels increase so must CO2 levels! That's how plants breathe just as humans do. Take a five gallon bucket, fill it 3/4 full of warm water, add 6 cups of sugar and 1 tablespoon of yeast and mix well. Drill a hole on cover and run a 1/4 " hose through top to your fan. Ensure the hose does not go in bucket solution! Plus make sure Lid is on and hose is air tight. I usually take some putty put it around the hose opening. This will provide you with 2 weeks of CO2 and must be changed regularly or when you fertilize your babies; because the yeast is eat away at the sugar and cause it to turn into alcohol. Make sure that you change it out and keep lid tight and run tubing to fan source. Good luck!

Make sure you are running 18/6 light schedule, soil is moist and you mist your babies with water every 3 days. You have just created or replicated the natural outdoors and this will stimulate your babies to grow. That and the CO2 method will definitely make your plant grow like crazy! You will see results in 2 days. It will be as if your plants are on steroids!

looks over-watered. maybe poor drainage. leaves look puffy and engorged, plant looks a little stunted.

bump
I put 5, 2 liter bottles with yeast and sugar water in there, u can tell the plant liked it.

but the leaves are still yellowing and now turning brown.

CO2 may make the plants grow faster, but you can only grow as fast as the weakest link in the chain. The plant needs to be fed nitrogen, bad. This is the cause of the yellowing and why the cotlydons fell off. By forcing it to grow faster, you have to feed it more.

what's that on the leaves? is it soil or some type of pesticide?

looks time for a 1/4 strength feeding

havn't started nutes yet
heres update
which brand nutrients do u recommend