Leavesare turning yellow then brown.

My girls are Russian Rocket Fuel from Short Stuff started Jan 1. Over the last week they have started to turn yellow on leaf tips and edges browing with time. My PH is 5.9. I am using Hydroponics system bubbleponics also, but the real term is “Water Culture.” I have a problem with humity at 30%. My grow area is 2'x2'x3'. Any ideas to bring it up. Please help my girls. All ideas are welcome. Thanks

Ppm too low, double it at least.

ph is a little low, also looks like nitrogen deficiency to me, maybe up the nutes a quarter strength.