Alkalinity (meq/L) - General Hardness (dkH): With working at a fish store since I was 14 there is one question I've encountered more than most. Why does my pH drop and what can I do to fix it? Most get confused when I tell them you generally don't fix pH directly but instead test and correct your alkalinity. To put it relatively simple terms the alkalinity of a solution, in a reef tank it would be saltwater, refers to its' ability to counteract drops in pH. Drops in pH, for example, can be associated to general day to day biological breakdown of nutrients. The higher your alkalinity the more likely you will be to have a stable pH value. Fairly simple there but then you have to look at the 2 most common scales used to check you alkalinity level. One measurement is read in milliequivalents per liter. The other is measured as degrees of carbonate hardness. Conversion from one to another is pretty simple. If you have a meq/L (say 2.5) and would like it in dkH you would multiply the meq/L by 2.8 to get a dkH value of 7.0. The same applies the other way. A dkH value of 7 would need to be divided by 2.8 to get a meq/L value of 2.5. Natural seawater has a meq/L value of 2.1 to 2.5 (dkH of 6-7) but most captive systems should be a a value of roughly 2.8-3.2 (dkH of 8-9). I keep my level at around 12 dkH. My clams and stony corals seem to do much better that way. Please refer to the next section for dosing recommendations.
