Bird my man, time to get out the growbook and read up.
While it's true woodash will raise pH, lime will NOT lower pH unless it's way above 7. It's a good buffer against wild pH swings though, that's why it's in Promix, Sunshine mix, etc.
Running an intake fan without an exhaust fan/filter combo will blow stink all over the house. In a 4x4 tent, a 6in Vortex with the proper filter will exhaust/cool/scrub very well as long as the ducting has a minimum of bends. Passive intake is best, just use a damper to keep the stink in when the fan is off.
I get my plants started under CFL and then once they get going, I switch them over to the grow cabinet. It seems every time I do this the plants start yellowing out from the bottom, curl up and die. If you look on my other threads, I show pictures of some of the symptoms starting. I water them every 3rd day and haven't introduced nutes until the plant is well established, probably 3 weeks into the grow.
Start feeding earlier. Yellowing from the bottom up tells you it's deficient in a mobile nutrient. Most likely Nitrogen.
My question; is 400w too much for such a small grow cabinet?
Too little actually, 1000w will fill that space completely. Obviously you'll need bigger or separate fans to cool and scrub.
I set the light ~4.5 feet above the plants during the entire grow.
Once they're 10in or so tall, 14-16in away is best for a 400W.
I was thinking it was nute deficiency but wasn't sure, kind of hard to tell. I was using Blue Mountain Organics but I don't think they contain enough N-P-K to support growth, especially under such extreme conditions
You may not need different nutes, maybe just mix them a little stronger. Actually these conditions are quite normal
Hope this helps,
Fred