I think I solved for my inability to control the pH. I've done 2 other grows (one coco; the other supersoil) and, now DWC. I tried tap water, then RO. Only when I switched nutes from Fox Farm (hydro) to GH am I able to control the pH.
Now: using tap water, GH nutes (according to Nebula's feeding schedule), checking water 2x daily (no adjustments needed last couple of days) for pH and ppm.
Moments ago, I topped-off the reservoir with the same. pH 6.3, ppm 534. Most importantly, pH is STABLE!!! Finally! F*CK!
DankwingDuck what should my ppm be at 3-4 weeks? I've read countless versions. What do you add to RO at the seedling stage? My RO water is bottled, from WallyWorld @ 89 cents/gal. Always 7.0. The roots are nice and white - not able to upload photos now, not sure why (not this site). There isn't much in the reservoir - very clean but, a bit cloudy. No sediment on the bottom. The roots look really good.
D.A.A.S.69 Ain't no rain in this part of the country for the time being. I'd love to use rainwater!
NAKEDGARDENER I love this GH waterfarm set-up with the drip ring. Works like a champ, despite not being terribly valuable well into the grow. There's no disadvantage, I can see, in using it throughout the grow - especially if you don't have much opportunity to water her throughout the day. I bought mine in a kit, from Amazon, for about $50 - all inclusive. I have zero motivation to build my own although do appreciate and respect that others do. It's a preference thing.
Thank you ALL so much for your encouraging words and helpful advice! I'm looking forward to a better grow and result with this grow. I get a lot out of the variety of advice I get through here and, whether I follow some, any or all of it, it's all valuable to me as it's helped me troubleshoot my problem. Thank you again!