Got a deficiency problem. Need some advice!!!

-The medium is from fox farm ocean forest soil
-They are under 600 MH and is on a 18/6 light schedule.
-Finishing up 3rd week of veg.
-I'm using under half of the recommended amount. Around 700 ppm, pH going in at 7.5 and the runoff is around 6.2
-I'm using x-nutrient micro,grow, and amino blast all @ 10 mL per gallon. I've called the company to double check... they said its all good.
-Additives are root excelurator @ 1 mL, voodoo juice @ 3 mL, and b-52 @ 3mL
-R/O water pH is around 8.0 ppm 0
-RH is around 55% @ 78 degrees during lights on, and 60% @ 60 degrees during lights off
-Noticing so far stunted growth on the bottom branches and leaves.
Red stems showing up toward the top part of the plant, bottom so far is still green but I don't think for long.
Branches on older fan leaves started to turn red first.
*From what I have read, I think it's N-P-K deficiency. But I want to here your input.... let me know if I left anything out.

I would cut back on your nutes and see happens. FFOF has fertilizer in it and you could be overloading and causing a lookout.

I think you are right. I recently transition back to soil from hydro and I forgot that the soil already has fertilizer in it. So instead of giving it plain water. I started off with nuts @ 1/3 strength, luckily i didn't burn my plants.

*Plus I did some more reading and found this on some other post:

"I use Fox Farm soils and don't even think about adding any nutrients until about the 4th week, and then only about 1/3 of the recommended dose. I then wait about 2-3 more weeks and give a full dose before heading into 12/12."

So I was wondering... To solve this problem do I just give it plain water on the next feed and dial back on the nutrients after that?

And the problem with your plant is? All I see is a normal healthy plant. Red stems is usually a phosphorous problem. But really your plant is fine as genetics play a big role in color of stems as well.
In this thread the person has red stems as well. https://www.rollitup.org/general-marijuana-growing/755063-aquaponics.html#post9863090