Keep it acidic like below 6.5 and you'll be fine. Certain nutrients have optimal absorption rates as far as PH. I know that calcium doesn't absorb well below 5.8 but more important then that is phosphorus doesn't absorb well above 6.4 it cuts off real fast. When you get a plant too high in ph often you'll see phosphorus deficiency and it's often mistaken for calcium deficiency since both cause a bit of brown spotting. When magnesium is locked out it will cause other issues many times that don't necessarily point to magnesium as the culprit. Ph is important. Almost any time I find a plant looking like it has an issue it's the ph that's off.
What people don't seem to understand is that there is no perfect PH. You should be utilizing a range of PH levels. Each nutrient absorbs optimally at different PH levels. In coco, I shoot for 5.6-6.2, never using the same ph level twice in a row. That gives you a spectrum of nutrient uptake.
Great point and I've brought up many of those nutrient ph charts and some of them vary a bit. I like 6.0. It serves me well. When my plants drop into the 5's they seem to get unhappy. Maybe it's just me. I tend to run it slightly higher then recommended.
I used distilled white vinegar in hydro until I bought some PH down for some time. It works but takes quite a bit. The plants don't seem to mind it. Once you get ph down you'll notice that it's powerful as hell. I went from putting a few ml's in to counting drops when I bought ph down. With my tap and recipe it takes about 7 drops of ph down to put me in range on average with about 2 gallons.
I use PH Down, but I dilute it to 50% strength. It makes fine tuning PH much easier. I also mix up 6 gallons of nutrients at a time (generally going through ~20 gallons of nutrients in a single feeding).
Damn 20 gallons? You must have a massive grow. How many plants are you flowering? I'm budding 4.. lol. I make my nutrients a gallon at a time every night. It's a chore. When you have staggered plants of different strains you have to custom each batch to get it right.
7 plants, each in a 5 gallon pot. Each one gets ~ 2 gallons a feeding once a week. I do drain to waste, so basically, each feeding is a pseudo-flushing of the coco. I never have problems with nutrient lockout or salt buildups, and the nutrients I use are relatively cheap and concentrated, so a little goes a long way. Using this method I only do a true flush twice a grow, once the first few weeks of flower, and then one more the last few weeks. I always give them whatever they need and feed until I get about 30% runoff into a drain bucket that I end up pouring in a rain barrel outside for use in the garden, so the nutrients don't go to waste. The plants pictured are about 4 weeks into flower. There may be better ways of doing it, but I've found this is what works for me.