To understand lock out you need to understand buffering, the electrical attraction of ions and pH. A simple explanation dealing with just basic (high pH) buffering portion: At low pH ie below 7.5 nearly all carbonates are bicarbonates (HCO3−
. They neutralize negative ions (basic pH causing ions). Initially bicarbonates are formed from carbonic acid (H2CO3), which is formed from dissolved CO2 in water. This quickly turns to Bicarbonate.
The bicarbonate is the actual buffer. What is attached to that buffer is what is consider locked out. Bicarbonates are formed in water, very few are available as salts. For example Potassium bicarbonate is only formed in water it is not in nature found as a salt.
Back to the subject. bicarbonate typically forms up in pairs (HCO3−
2. This means it has a negative 2 charge. With a negative 2 charge that means it will glom (nice scientific word) onto a cationic ion with a two charge. IE it will draw a Ca++ or a Magnesium++ cation usually. Ca++ has a stronger charge than a Mg++ as it has a larger radius so typically the bicarbonate ties up the Calcium, especially as there is more Calcium present than Magnesium so it has a greater chance of bumping into (another great scientific expression) a calcium ion than a magnesium ion.
A Potassium ion has only a plus one charge and simply can not compete as well in forming up with the bicarb unless they are in high numbers. Hence some manufacturers use a lot of Potassium versus a lot of calcium so as to have the excess potassium tied up instead of calcium and magnesium. Now the bones of the story: every time more + ions are taken up by the plants roots IE nitrate, a carbonate ion is released which gloms onto positive charged ion(s). IE tied up + ions and a higher pH as the balance has switch to less excess H+ protons.
The out of wack pH is simply a result of releases of H+ or (HCO3−
by the roots in order to maintain a ionic balance. This causes a pH changes as pH is basically dependent on the amount of H+ protons above the number of OH- ions. This means if there are more extra H+ protons your pH will be acidic and if there are less H+ than OH- the pH will be basic (above pH 7). This is directly related in our nutrient water to the level of buffers so that directly ties in with the tied up ions. The tie up is also related to the fact that a 2+ ion has a strong attractive/holding force so it does not readily let go once formed into a bicarbonate compound.