Kh is a measure of alkalinity, obviously. Alkalinity can also be measured in ppm or meq, different units for the same measurement. Alkalinity, in whichever unit, is a measure of a solutions ability to buffer a drop in ph. The higher the alkalinity the less a solution wants to change ph, i.e. it has a high buffering capacity.
Were you to take a solution with an alk of 20 Kh it would take a considerable amount of acid to drop the ph a significant amount. Whereas an alk of 0 Kh would require very little acid to make the ph plummet. This is a simple synopsis of what is going on but you get the picture. Again the whole thing is far more complex but that is the jist, sort of, lol.
Keep in mind that alk doesn't determine the ph, it just buffers a change. I have seen very low alk water that tests at ph 8, and high alk water 8 kh or about 140ppm (which really isn't that high, my well tests at 300ppm), that tests at ph 6. But, one drop of acid in the low alk ph 8 will drop ph big time, whereas the 8kh water will only drop a little bit. It all depends on the volume of solution, of course, and the strength of the acid, as to how much of ph drop will occur. Once you hit zero alk acid makes a solution go down fast, real fast. Most my experience with this has been in the greenhouse industry, so anybody with anything to add more specific to reef tanks please correct any errors on my part.
I'm really wanting to understand how one parameter can affect the other. For example: how does high or low Kh affect Ph?
If my Kh is 11 and my Ph is 7.8 what is affecting them for the readings to be off? Aside from a test kit.
Kh stands for alkalinity right? Specific hardness?
I've never been very good at chemistry but that was back when I had no patients. Now I do and I want to learn.
Any suggested reading I can do online?
The chemistry behind pH and alkalinity can be complex, but there are easy ways to remember what we, as reefers, need to do to balance the tank chemistry.
dKh is short for carbonate hardness and is often used as a unit of measurement for ALKALINITY. Other common units may be as meq/L (milliequivalents of solute per liter) and ppm CaCO3 (parts per million of Calcium Carbonate).
When the reefing community talks about ALKALINITY expressed as dKh, ppm or meq/L, the discussion is really about the buffering capacity of the water relative to pH changes. We use sodium bicarbonate (NaHCO3) from baking soda and Calcium Chloride (CaCl2) to provide the buffering capacity and calcium requirements of the reef corals. Simply put, the carbonates that are formed prevent large swings of pH from occurring, that is, they provide a buffer against pH swings. The larger the dKh value, the higher the buffering capacity. The health of the corals and fish is maintained by having a stable pH is due to the buffering capacity of the water. Alkalinity slowly decreases over time due to the nitrates that are formed and the CO2 in the air. These form acids that react with the buffer....as the buffer is used up in resisting a low pH swing, the dKh decreases.
pH is a unit of measurement that describes the water in terms of acid (<pH7), basic (>pH7) or neutral (pH 7). pH is logarithmic where a pH of 7.5 is 10 times more acidic than water at a pH of 8.5, so small pH changes may have a significant health impact on fish and corals. To add to the confusion, alkaline is another description of a basic pH, but is not related to the term ALKALINITY (see above).
Hardness, often expressed as General Hardness (GH) refers to the dissolved concentration of magnesium and calcium and other ions. Units of measure include dH (degree hardness) and ppm (parts per million). You probably know about this as water is often described as hard or soft. Hard water often comes from limestone aquifers that contain calcium carbonates.
There is a strong relationship in the triangle of pH, hardness and alkalinity. When you adjust for one parameter, you affect the other two, making it very difficult to make adjustments. It is possible to make minor adjustments, but you need to know what to do and its impact on the other parameters.
For instance, when you add lime water (Kalk) to the tank, you are increasing hardness and alkalinity, which increases the pH.
If you add just baking soda (sodium bicarbonate), the alkalinity will increase and the pH will try to equalize towards pH 8.2. Note that if you heat the baking soda in the oven to drive off the CO2, then add it to the tank, the pH will have minimal effect, but the alkalinity will increase.
Confused yet?? I have seen many perfectionist reefers go crazy trying to get the "perfect" water chemistry parameters. Test for alkalinity and calcium and don't worry too much about pH. (pH changes over the course of the day and night cycles as well as when supplements are added) Maintain the calcium and alkalinity, check for nitrates and perform periodic water changes. Every once in a while, the calcium/alk balance goes out of whack and you may need to do a large water change or re-balance the supplement dosing.
Here are some additional reading articles if you want more information:
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