DWC Auto Help Please

I recently left my White Widow Auto for four days and came back to what I thought might be N deficiency as the lower older leaves had wilted. The PPM was at 140 and the PH had risen to about 6.7. This is my first run with DWC and anything hydro for that matter. I'm using General Hydro Flora series with Hydroguard. Here is the environment.

Dinafem White Widow Auto
5 gallon bucket 3 gallon res
Temp 69-75F
PPM 375 (as of now)
PH 5.8
2x4 Tent
400W MH
RH 45-55%

Any help or input would be greatly appreciated. If there is anything that I left out just let me know and I'll do my best to provide it.

If i had to take a stab at it id say it was the ph. Ive found that hydroton (no matter how much you rinse) will raise the ph eventually. Just keep an eye on the ph and from my experience, it does seem to maintain and level out. The veg stage is especially important. Im in week 2 or 3 of flower and i can leave my buckets for a few days and they are around 6.0 when i come back. Dont give up man. I messed up a couple runs by not paying attention to ph like i should and the difference is night and day wether its some mex bag seed or kill genetics

It looks like it wasn't getting enough nutrients due to low nutrient content and pH lockout. I'd maintain the 5.8 pH with a controller (if you can afford it) and raise the ppm of the res to 4-500 if you are not reaching equilibrium in the high 300s.

Also, raising the humidity to 60-65% wouldn't hurt. I would do your current RH in flowering.

dont raise the humidity to over 50%, that will cause problems because being in direct water with air coming up will raise the humidity around the bottom of the plant even higher, which could cause high risk of mold.

From the pics its a little hard to tell, because it looks like the plant has a nice green to it , unless the pic is darker and is lighter then what it displays, so it could be low nuits. However I grew alot of autos over a couple years and you will always see ph jump up and down but never seen a plant react that fast to that amount of leaf change in 4 days.

One other thing i can think of is that the leafs got wet and got burnt from the light, keep a eye on them to make sure water is not splashing up from to much air pressure. Just wondering how far away is the light from the plant.

Also Give the plant 20 hours of light, even threw flower because of the short time frame of the auto plant that 20 hours will help you push the most out of the plant you could get away with 18 but i noticed you get more with that extra 2 hours.

Also do not do any form of training stress to those plants because it will shock and will send it into flower, if you are going to do any training only do light tie down where the stem does not get any form of damages or anything cut off.