White Widow/Power Plant DWC

I added a little more of the Bloom with this weeks water change, the TDS dropped a lot this last week so I figured they could use the nutrients. I scored a huge portable AC for $100 so I took the chiller out of operation for the time being temps are staying around 72 only slightly above the house temp. I'm experimenting with the light angle and also the additional LED to try and get light to all the important parts which is really difficult with the PP cola being a foot taller than the rest. I'm really seeing the limitations of the 400 watt with this grow, and I'll be keeping an eye out for a deal on a 1000 watt ballast now that I know i can control the heat. The White Widows are really looking impressive, and they aren't even getting the amount of light they deserve. The power plant looks like it's going to be slower to mature just by comparing the two. The scent is getting incredibly strong and it's mainly coming from the widows. Today is (11/10) and day 29 since beginning flower so were pretty close to the half way mark. Hopefully I don't screw anything up before then. I'm already planning my next grow in this tent which is going to be 4 clones of the first Widow in this grow. I'm sure I can yield much more with an even canopy. Oh I almost forgot, earlier in the week when I opened the tent I noticed some strange symptoms on the lower leaves of the power plant, so the first thing I did was check the ph. Somehow it dropped in the 4's from yesterday being at 5.7 so I added tap water to top it off instead of RO and adjusted back to 5.7 from there. The leaves affected had round brown spots 1-4mm in diameter and slight yellowing overall. Will a plant show problems from such a quick ph change?