Hi @bejesus! Nice to meet you!
I’m not at all familiar with your setup as I typically grow in soil/coco. However, I say she’s looking a little dry. Could you give us a little background?
What is the beauty you have there?
What’s your room humidity/temp?
What have you done with her over the last week?
Any nutes on board? If so, what kind?
If this is the first time you have seen this occur, what were you doing previously and what have you done differently now?
Thanks for sharing! Look forward to seeing more, but if I don’t get to you in time, @MDBuds, @Mrb53004, @Rye, @Adcrag, @Kimmyann253 @Hippy1978 will be around at some point, it is growing season, so please be patient.
looks like your growing hydro? what light are you using? Theres alot of great growers on here that can guide you… & welcome!
If she is a New, recently received clone, sometimes the plant stresses becasue of the process it goes thorough from getting cut to grow roots. Yellowing is normal as we root in water and usually do not add nutes. It is not a seedling so it will need Nitrogen…It will need a full NPK fertilizer. Make a list of the solution in her tank, including the ph of the water and tds levels. Please itemize the nutrients that go into making the solution, if aerated and temp.
I’m using a Mars hydro ts600 for the light as well as a dwc bucket with air stones and clay pellets for my medium. As far as the nutrients go I’m using the fox farm nutrient line, and my temp and humidity stay at about 75 degrees and at about 50% rh. The ph and ppm levels are somewhat stable, where the ph fluctuates the ppm stays about the same until I feed them. That’s when the ppm starts to fluctuate
Sounds like you are on the right track. Keep your eyes on it. If the yellowing increases, there are issues. You did not state if you got it this way…Many of the clones I do yellow out until they establish themselves. Sometimes I make an ammonia spray to Nitrogen boost them
When I got it, it was green completely. And I think it was trying to flower because there was pistils forming already, could it be the stress from changing the light cycle to 16 hours?
When you are starting a clone you need higher humidity less leaf area. Cut or remove the yellowing leaf, increase humidity to 70% to help plant transpire easier, and increase your room temp. Leaf temp is typically 5dg cooler than room temp. You need to lower you VPD to allow the plant to use less energy breathing and more energy producing roots.
Stress can do many things…including yellowing
I assume you got her recently as she is not that big and the lower leaf has a clean cut. We cut our clone leaves to help rooting process.
Do you know the strain and genus…?
Photo period / autoflower
If she is photo and had pistils, means mamma was mature…If you take a flowering plant and UNFLIP (bring back vegging state), it takes about 3 weeks for her to settle in to the change. I would up the lights ON to 18 hrs
trim off the yellow cut fan leaf
Just watch carefully…Maybe someone who has more experience with HYDRO will step in. Hydro is tough as Ph fluctuates, aeration changes ph, water needs to be cleaned / replaced every so often. Hoses, stones, tubes…all need to be cleaned regualrly…
Ok thanks! And I’m pretty sure she’s a photo but not to sure of the strain
Exactly why I haven’t tried this. Seems like too much of an ALS pt to me. What would be the benefit to this sort of setup? In my head, I think it would require exactly like you said, but wouldn’t someone have come up with some sort of something to prevent buildup? Apologies for the lack of correct words, not much sleep. First, I’m like saline, then I’m like, not at all. That would equal dead plants lickety split.
Also, it’s been a while so…every time I see the heading on this post…Me: “Let’s Taco 'bout it!” 
Hydro for how BIG, Fast, potent it can make the plant. Nutrient go directly upstream…It is like mainlining if you were a junkie
Or giving an IV push in friendlier terms. Sorry, had to talk it out to exchange images.
I guess you can tell which side of the street I grew up on… 
Same street, no shame. My PTSD isn’t your responsibility. I chose it.
Also, really they are just alkaloids attracted to their mates, aka receptor sites or MAGNETISM if you will. It’s easy to hold the arm up if you want quickness, level for normalcy.
@kmac03 they do make hydro amendments that prevent build up. They also have hydro nutrients that are salt less and organic that don’t leave residues or clog lines or sprayers. They’re usually more expensive but worth it because then all you have to worry about is the weekly maintenance. Check lines and stones for mold/mildew/algae, gresh res, fresh nutes, and a ph check.
Sounds like a job for the checklist. 