First grow, yellowing leaves

I've got my first grow going. Already have made several mistakes that I've learned from. I'm growing in a pro-mix and worm casting mix. I started in the nursery grow bags and have recently transplanted to the 5 gallon. I'm using a mars hydro light that until about a week ago I was running 24/7 but over the last week I've switched to a 18 and 6. I'm watering every morning (rain barrel water) with a iguana nutes included every time. Tent temp I had at 80 until a week ago but now trying to keep it at 77 unless light is off and then it's around 68. Humidity has been between 40 and 50%.

I have yellowing leaves. My current guess is that I'm watering too often but not enough (thinking of water ing more thoroughly and then waiting until. Dry)

I also wonder if I've had my light on too high, I certainly think I've had it on too long.

Thoughts?

Your idea to change your watering method is likely a big part of it. See how a deep watering changes its appearance.
Then Id sprinkle some dolomite around it to, and some casts or compost top dressed or extracted. Those 3 things are very mild acting in that you wont burn or cause harm using it to figure out if it remedies the issue. But they are like medicine for sick or unhappy plants (heat stress, any stress they dont like!). And oh the microbes!
Thats my opinion. Just think about, look into it and make a choice your comfortable with.

This will help too

Helpful advice, thank you. Because the plants are in early stages I'm using a 2ml per liter of water of iguana nutes. Do I continue that when doing a deep water? I haven't heard of dolomite, what is it bringing to the table?

Do a deep water. A moderate amount of water let drain, wait 10 minutes, again moderate, wait and by the third time the water should stand on top of the soil and drain out the same rate as the runoff from the bottom. Wait till the next day....
Then if you want the soil is optimally moist for any liquid ferts.
I don't know Iguana brand or specific strength so I wont reccomend anything.