Yes...THAT's the better pH chart Red !
And this is a good discussion / debate topic.
Keep in mind that I'm talking about chem hydro nutes, taking into account that the solution pH will drift within a soil less medium very similar to the pH drift experienced within a recirculating hydro reservoir. I see everyones point about promix being more like a soil medium than a hydro inert medium like lavarock, lecastone, rw or even coco. But throw in the 20 to 30% perlite most folks use and it's suddenly closer to being a high drain inert soil less medium.
Yes, the added dol lime helps buffer the pH from going too low, but in that it's usually sending the pH upward within the medium giving the roots exposure to that drift in pH range. Until the lime is exhausted in the medium, the higher the pH going in will cause the higher pH drift in the medium, which will be a tad higher than what is seen in runoff pH. Or said another way, if it goes in at a solid 5.8 it's more likely to run off closer to the levels where chem hydro elements become much less available. In some ways, if a soil pH test is run the pH found is even higher than what's being seen in the run-off. Later in flowering when the plants are taking in more P than N, that drift may head the other direction, but most growers end up "treating" that by watering in more lime, turning the drift back around and upwards yet again.
Why should the grower chop in half the availability range by setting the initial pH at in the middle or near the top end of the usable range with a start at 5.8, thus letting the pH swing towards what is a danger zone if he's using a chem hydro nute package ?
Getting off more toward a chem nute solution in recirculating hydro purist thought wave..
Not much emphasis is put on Plant nutrition by "mass balance". Mass balance speaks to the fact that plants uptake different elements from the chem solution in hydro at different amounts and differing speeds, leaving behind or taking up more slowly or at lesser levels other elements on their dinner plates. Metaphorically speaking, if you give a child a daily dinner plate with several items on it...say a double quarter pound cheese burger, veggies and a big piece of chocolate cake...chances are he's going to slam down that cake first, then the cheese burger and not touch the veggies. If however, that plate has a smaller cheese burger, smaller piece of cake and the veggies...chances are alot better for him to eat everything on the plate.... Now look at the pH chart for hydro or soil less mediums and draw a line straight up from the 5.8 area to the magnesium and it becomes more clear why so many growers see mag and various other micronute and even P & K defs.
My point (very much up for discussion btw) is that...
Hydro and soil less mediums are certainly NOT flat line like the soil pH chart shows and don't buffer anywhere near the same as soils.
Chem nute packages are very prone to elements percipitating in solution and in inert soil less mediums....above 6.4 is the "danger zone"
And... "there's more than one way to skin a cat" :-)
Arrgh, I'm way over tired and have more thoughts on this but need rest...talk later.
Last edited by 10k; 05-13-2009 at 01:14 PM..