That's typical tip burn that's very common with lettuce. Some varieties are more susceptible than others. It's a calcium deficiency but that doesn't mean you don't have enough Ca in your solution it only means that the plant isn't getting enough out to the leaf tips or to new growth very well. Your Ca levels may very well be fine...or not.

Couple things you can try is to give it less light (duration and/or intensity). Lettuce grows very fast and if you give it too much light and accelerate growth too fast the plant can't keep up with transporting Ca. The other thing is you can try to get some more air flow on it. That will increase transpiration (water uptake) which means the plant will uptake more Ca. Lastly, you can increase your Ca levels although it's rarely a level issue and usually a growth and transpiration issue.

That video I posted a little while back of the romaine in the mason jar started showing signs of the same exact thing. I moved it further from the light, upped my Ca levels a touch and made sure it was getting more air on it from my fan. Basically correct all the possibilities and that took care of it.

It's so common with lettuce that there is even a lettuce tip burn scale and rating they use for commercial production.

Thank you, Ive since added a tower fan to my grow tent so it should help with the air. I will try upping the Ca at the next nute change and i can dim my light down for now.