i like that you are trying to understand and not just follow directions, so here is my attempt to explain ph: skipping the actual definition, the way ph is measured is thru a balance between the positive and negative (hydrogen)particles floating around in liquids ready to find an opposite charged particle to interact with. this is important because its not only the negative to positive ratio but the actual amount of particles that come into play when trying to understand the practical implications of how ph behaves.
every single thing you put into the solution: gas solids or liquids will introduce a new range of free charged particles that will alter the ph balance, oxygen brings the ph up, carbon dioxide brings it down, most nutrients are acidic but calcium nitrate (calmag) and other minerals are alkaline.
the key to understanding ph is that ppm is as important as the ph value itself. ro water has a very volatile ph because it has nothing in it so any gas exchange will mess with the ph, hard well water has a very stable ph because its loaded with salts that act as a buffer for the gas exchange. this means the higher the ppm the more stable the ph of the solution
now imagine two different solutions;
one with 10 negative ions and 100 positive, being a 10 to 1 ratio means the ph would be 8
the second one has 100 negative ions and 1000 positive ones, also a 10 to 1 ratio and the ph would also be 8
but what would happen if we add 100 negative ions to each solution;
the first one would have 110 negative and 100 positive changing the ratio to pretty close to 1 to 1 bringing the ph down to 7
the second one would have 200 negative and 1000 positive with a ratio 5 to 1 bringing the ph down to 7.5
this are made up numbers, the real numbers behave just like that with a ton of more ceros, each ph point is then times more (acidic or alkaline) that the previous value: 6 is ten times more acidic than 7 and 5 is ten times more acidic than 6 and 100 times than 7 and so on.
so finally if you want some practical ways to exploit this to your benefit id suggest dissolving some acidic salt that will 1) benefit your plant because its a nutrient, 2) lower ph to the desired value because it going to be acidic 3) provide enough ppms to buffer any environmental factor that could mess with your ph
i love monopotassium phosphate (mkp for short) but may be too much for veg so i would use potassium nitrate for soil grows. minimum quantities just enough to raise the ppm of your water enough to drop ph to 6.5 and provide ph stability, maybe 50 or 100 ppms, youd have to try to figure out exaclty how much. another thing you can do is take a small jar or something to scoop some water from the bucket and pour back from 2 to 3 feet high over and over for a minute or two to aerate and dissolve oxygen back into your water, bringing the ph drift caused by carbon dioxide back in place.
hope this helps you understand why some water needs constant adjustment and others can be pretty stable, its the ppm
