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Discussion Starter · #1 ·
Angry John recommended these two readings on the subject of pH, calcium hydroxide and alkalinity:

Questions are
(1) What is preferred test kit for alkalinity?
(2) What is preferred range of alkalinity parameter (meq/L)?
(3) If everyone else understands these concepts clearly, ok; otherwise, do you think it possible that the topic could be discussed again at Freddie's KBMAS February meeting?

Although I read the above articles, I admit that my understanding drops off sharply after the pH concepts of log scale and H+ vs. OH- concentrations. (I am continuing to self-educate and read articles on this subject.) However I got that
(1) a drip of Kaltwasser or a slurry in the sump would increase the pH as it added calcium hydroxide.
(2) I understand that the alkalinity must also be controlled so that the pH is not so difficult to adjust.
(3) The type of salt used may affect these variables. I use Oceanic Natural Sea Salt mix. (When used up I will switch to my other container: Reef Crystals.)

Measured my pH again today and used a Tetratest Laborett (can you really trust a product with a name like that?) to measure alkalinity. The kit used a unit called "dGH" for marine (carbonate hardness); I am guessing the unit is similar to "dKH".

My tank parameters are
pH: 8.0 (slightly higher toward 8.2)
Carbonate Hardness/alkalinity measure: range 7 to 8 dGH, converted to range 2.5 to 2.86 meq/L

I conclude, with my limited understanding, that the pH should be raised and the alkalinity measure would be better higher as well.

So I am going to add a small amount of Kaltwasser slurry to the sump. I am not planning on doing anything with the system buffer at this time.

311 Posts

General hardness is primarily the measure of calcium (Ca++) and
magnesium (Mg++) ions in the water. Other ions can contribute to GH
but their effects are usually insignificant and the other ions are
difficult to measure. GH will not directly affect pH although "hard"
water is generally alkaline due to some interaction of GH and KH.

GH is commonly expressed in parts per million (ppm) of calcium
carbonate (CaCO3), degrees hardness (dH) or, more properly, the molar
concentration of CaCO3. One German degree hardness (dH) is 10 mg of
calcium oxide (CaO) per liter. In the U.S., hardness is usually
measured in ppm of CaCO3. A German dH is 17.8 ppm CaCO3. A molar
concentration of 1 milliequivalent per liter (mEq/l) = 2.8 dH = 50
ppm. Note that most test kits give the hardness in units of CaCO3;
this means the hardness is equivalent to that much CaCO3 in water but
does not mean it actually came from CaCO3. Water hardness follows
these guidelines:

0 - 4 dH, 0 - 70 ppm : very soft
4 - 8 dH, 70 - 140 ppm : soft
8 - 12 dH, 140 - 210 ppm : medium hard
12 - 18 dH, 210 - 320 ppm : fairly hard
18 - 30 dH, 320 - 530 ppm : hard


Carbonate hardness (KH) is the measure of bicarbonate (HCO3-) and
carbonate (CO3--) ions in the water. In freshwater aquariums of
neutral pH, bicarbonate ions predominate and in saltwater aquariums,
carbonate ions begin to play a role. Alkalinity is the measure of the
total acid binding capacity (all the anions which can bind with free
H+) but is comprised mostly of carbonate hardness in freshwater
systems. Thus, in practical freshwater usage, the terms carboante
hardness, acid binding, acid buffering capacity and alkalinity are
used interchangeably. In an aquarium, KH acts as a chemical buffering
agent, helping to stabilize pH. KH is generaly referred to in degrees
hardness and is expressed in CaCO3 equivalents just like GH.

When the aquarium has some carbonate buffering in it, the
bicarbonate ions will combine with the excess hydrogen ions to form
carbonic acid (H2CO3) which then slowly breaks down into CO2 and
water. Since the excess hydrogen ions are used in the reaction, the
pH does not change very much. Over time, as the carbonate ions are
used up, the buffering capacity will drop and larger pH changes will
be noted. From this it is clear why aquariums with low KH seem
unstable - as acid is produced by biological action, the KH is used
up; when it is gone, the pH is free to drop rapidly as H+ ions are

The gh is a measurement used in freshwater aquariums and is not directly applicable to use in a reef but will give you a round about answer as to where you stand. I would only use a buffer before making up your salt mix to raise the ph and prevent the carbonate ions being used up in returning your ro water back to neutral...

311 Posts
Alkalinity is a seldom-understood water parameter. It is also known as carbonate hardness (KH), and thus allows for confusion with the term General Hardness. Make no mistake GH and KH are two separate measurements. As we discussed in the second article, GH measures how many cations are in the water. Alkalinity, on the other hand, measures how many anions are in the water. An anion is any ion, which has an overall, negative charge. These anions react with any acids (H+) introduced into the water, thus neutralizing them and maintaining a high pH. This is where the definition of a base as a proton acceptor comes into play. Actually, many people consider alkalinity as the total amount of base present in water. In aquariums the most encountered constituents of alkalinity are: bicarbonate and carbonate. We can then define alkalinity as water’s ability to absorb acids without affecting pH.
Alkalinity has three different sets of units, which are the most frequently encountered in the aquarium trade. In the United States Parts Per Million (ppm) is most prevalent; whereas, in Germany, Degrees of Carbonate Hardness (dKH) is the unit most often used. Finally, a more scientific unit, is: Milliequivalents Per Liter (Meq/L). Even though these three measurements have different origins, I have seen all of them used in aquarium literature, without any sort of rhyme or reason. Here is an easy way of converting these units:
50 ppm (mg/L) = 1 meq/L = 2.8 dKH
I hate to sound like your mother (sorry GCAS moms) but: I cannot stress enough, in each one of these articles, that any creature which we maintain in our aquariums has evolved to deal with water parameters in a certain way. Alkalinity actually helps us respect this inevitable truth in many circumstances. Fish waste is acidic by nature, and will therefore slowly lower the pH in an aquarium. However, if there is an abundance of anions in the water, these chemicals, which contribute toward alkalinity, will react with the acids and neutralize them before pH is affected.

407 Posts
Discussion Starter · #5 ·
Thanks. I'll work on getting these concepts down.

I, for one, appreciate mothers ... and I do agree that aquarist have a responsibility to try to provide a healthy ecosystem.
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