2nd Grow Purple Stems - Plants Looking Sad

So I am moving on to my second grow. I have 4 plants growing in two separate undercurrent systems. I built this system based on the issues I had with my 1st grow where I did just basic DWC in 5 gallon buckets all sharing 1 rez. I spent alot of time planning this out but am immediately having some issues that are concerning. I use Well water that is ph 7.0 and ppm of around 125 for my water source. I have a 600w MH/HPS and a MarsHydro SP3000 in my room. I use GH Flora series. all 3. I also am using CalMg and UC Roots to keep a sterile rez. (switched to this vs Hydroguard that I used in 1st grow) Each system is using 24 gallons of water in total. Temps are mid 70's RH at around 35-40%. After adding nutes I am at around 500PPM. 1/2tsp/Gal of Micro/Grow/Bloom and 1tsp/Gal of CalMg.

I moved the plants from their seedling box to the new system about 5 days ago. Two of the plants in System 1 are doing ok. they were stressed from the move but are growing and look fairly healthy although plant 1 has some light purpling but not bad. the other two plants in system 2 are not so good. they are growing slowly and both plants have very purple stems and saggy leaves. just look sad in general. I should mention though that the roots on these plants are growing rapidly. they are much bulkier than they were 5 days ago when I moved them. its the top side of the plant that is looking not so good.

In using this new system I am noticing that I am having a hard time controlling PH. I thought having a higher volume of water would make this easier to manage but that has not been the case. I am wondering if the quantity of water and the associated heavy metals are acting as a buffer to my PH down. when I change the rez, I am at an even 500PPM and 5.9PH. each morning when I check levels, the PH has raised to 6.5 or higher and I have to add more PH down. What is causing this? I did not have this issue when I was running smaller rez and buckets. I am thinking this may be causing the purple stems but did not see this issue in my 1st grow where everything was great throughout veg.

So first question is what do people think is causing the purple stems and veins? all 4 plants are same strain, White Widow / Big Bud.

second question, when you try to adjust for a problem, how long should I expect it to take for the plant to show signs of improvement? I have 0 experience so I am not sure if I am looking for improvement in hours, or days, or weeks.

3rd question, do you have any tips or suggestions to make my setup better?

any insight would be great! Thanks!

Update... the larger rez just took a few days of adding ph down to balance out. Once I got it stable it's run like a champ. So for others going to a larger water volume. Don't let the ph spikes get you down when you change rez or fill it for first time. Just keep testing and adjusting and it WILL stabalize. The harder the water, the longer it will take to stabalize is my guess.

Just did the 12/12 flip. I can't prune these ladies enough. They replace leaves as quickly as I can take them off!! The two on the left are gonna be something special I think!!

They’re growing nice! I’m running 2 separate strains however in soil. Exact same environment and feed/water. One has all green stems while the other has red/purple. Although it could be that the one showing color needed more of something, I chalked it up to genetics as it’s Blueberry strain and have been known for this. Sunburnt stems and low temps can also cause this as well. Yours look damn nice though and aren’t having any problems! Just enjoy the colors !

The red/purple stems can be genetics but most commonly are a P deficiency caused by problems with PH just like you said you were having. The PH problems you were having most likely cause a lockout of Phosphorus being taken up by the plant. Starts as red/purple stems then yellow leaf edges and splotches on leaves then leaf tips curl up and dry out. Get the PH dialed in and give it a good feed and it will be fine.