Feel free to offer advice! Most helpful gets selec...

@StinkyPinky First of all that's a hell of a first grow so far you have clearly did your research. That being said Ill ignore all the basic stuff you already have figured out anyway like PH and move the thing I wish I was told before doing DWC lol. If you notice the growth from weeks 3+ was insanely good compared to the first 2, this was because of where the rockwool/seedling was placed inside the net pot. If you place those little guys lower in the netpot their roots will be so much closer to the water and LITERALLY save you 4-5 days of grow, because the airstone causes water to splash and soak the hydro-ton at the bottom of the net. Another thing that might help - If you thoroughly mix the water BEFORE adding nutrients/PHing it will break down the CarbonicAcid in the water drastically raising the PH - Do this every reservoir swap and your PH will remain stable for longer. Final suggestion which i'm sure you are aware of -- A SCROG! check out my Green crack DWC grow to see how much a SCROG actually helps. It allows you to lay your branches vertical so the buds grow horizontal utilizing the extra spread out light! I hope this helps man - to be honest your killing it so far and you only really need to quality of life tips at this point. 😎

Purpling of the stems is a sign of early magnesium deficiency. In flower, the need for mg is greater than the need for calcium. I would start replacing the cal max for epsom salts. Everything else looks fine, just keep an eye on the canopy during stretch so it keeps even.

only thing i can really tell might be a tiny bit off is that you want that lamp to plant distance not to be much over 16 and no less than 14 inches, this will help the plant grow bigger and faster. That's because the light gets focussed / diffused in an exponential way, a single inch has an outsized impact. You'll see ! Just make sure you keep checking at leasy daily the next couple of weeks as you'll want to maintain that distance during the flower stretch which is still ongoing. Hope this helps bro, looking tip top otherwise ! 🚀