Hi guys and girls,
A quick question about the pH of water and it's change over time.
Last night I was playing around with germinating in a glass of water, pH reading when I dropped them in was 7.5, this water was fresh out of the tap.
This morning tested again and it rose to 8.0, everything I've read says the exchange of co2 / Oxygen should make the pH drop?
Please allow me to suggest that you've slightly misunderstood what occurs with the gas exchange.
First, remember that water out of the tap often has many gaseous elements or substances in solution in the water column. The gas a water supplier does NOT want in any appreciable levels in solution is CO2 (it would make our water fizzy and could kill things, not to mention the worst issue) in large part I would guess because it causes pH to drop; i.e. acidifies the water column.
Second, we also know that O2 drives pH up.
The water right out of the tap was likely low in DO2 levels (dissolved O2, oxygen), or may have even been a bit high in CO2 levels.
Third, the exchange cannot occur where there is no air-water interface, k? Also, if the surface-area to volume ratio is sufficiently low the gas exchange may not occur well (think tall, narrow tube). So, if the DO2 levels were low, exposing the water column to air allowed those levels to come up sufficiently into solution so as to RAISE pH.
And again, if the CO2 levels were high, exposure to the air would allow it to dissipate from solution, which alone would cause pH to rise. However, reducing CO2 levels is also allowing the DO2 levels to come up, which would..? Cause pH to rise.
Depending on the
alkalinity of the water (alkalinity as defined as resistance to pH shift), different things may happen if the CO2 levels were sufficiently high in the presence of sufficient O2, but that kind of scenario really doesn't seem likely at all.
Also, is it a good idea to let water sit for a day or two before adding nutes and balancing the pH if this is the case with tap water? That's a big change overnight...
Yes, along with either aeration or some other form of water movement that would cause surface turbulence and agitation, because it further drives this gas exchange. It's not commonly known or understood in the cannabis world, but this mechanism and issue
is very well known and understood in the reefkeeping world.
Here you have this gigantic box of saltwater that you need to keep pH'd >8.0, must have high Ca levels if it's got hermatypic invertebrates (reefbuilding animals, corals and the like) and let me tell you, shifting pH causes dramatic issues with aquatic organisms! The shift you described is plenty good enough to kill a lot of things, quite a lot of things in my experience. So, what happens is the weather gets cold, so people turn on their home heaters. The folks who have the biggest problems with dropping pH in their systems often have oil- or propane-heated homes, and never realized
until they set up their systems that their heating was even causing CO2 levels to come up.
And then the tank acidifies and everything dies and it's completely and totally fucked. All because of the AIR in the home!
Gas exchange, I haz eet. Pull mah finger!
