ion behavior


New member
Questions for chemistry specialists!!!

By adding calcium chlorure you increase the amount of chlorure in the aquarium. at the same time calcium is used by corals and calcium decrease. then you add again and again calcium chlorure. and you always increase the amount of chlorure.

chlorures ions need to have link with other positive ions but which ones? knowing that at the same time you add no new sodium ions or magnesium or potassium and calcium decrease all the time.???????????????????????

i wonder how it is possible to increase th amount of chlorures without increasing positives ions.

Same question with bicarbonates:
people who put acetat in the aquarium get more and more bicarbonates. but i wonder how bicarbonates can increase and at the same time all other positives ions do not increase??????

More strong:
you increase at the same time chlorures and bicarbonates and other positives ions stay the same. how it is possible???

Mysteries of sea water or plausible scientific explications??????



Premium Member
There's no practical way to add calcium to the tank without adding any anions. Adding limewater will supplement calcium and carbonate alkalinity without adding chloride.

Here's the equation for the conversion of acetate into alkalinity:

CH3COO- (acetate) + 2 O2 -> HCO3- + CO2 + H2O


If calcium acetate is used, again, the tank gets calcium and alkalinity without chloride.

I don't know of any practical way to add chloride without adding a metal.


Bomb Technician (EOD)
Premium Member
i wonder how it is possible to increase th amount of chlorures without increasing positives ions

Real easy :)

Ca and Mg are used in great quantity by plants and animals. They also can leave solution as carbonates called abitoic precipitation. The chlorides have little use / say and the only way chlorides leave solution is if enough water has evaporated or you do a water change. Sodium is the same thing, as is Potassium, although Potassium is more used and can fall. Bicarbonate ions are also greatly used up. If any ion has very little biological function and you keep adding it it will increase. Sulfate is another - ion that does not leave solution easily.

Ions that find it hard to leave solution, due to their very low activity

Na, K, SO4, Br, Cl- and there are many others. NaCl or table salt will leave solution only if 90 % of the water has evaporated. CaCO3 when 4 % , K salts a 95 % and sulfates salts 20 %.

The only way of adding chloride, without a metal, is in the form of bleach where it can get converted to chloride. Such is the case when bleach is run through activated carbon. The chlorine bleach reacts with the carbon, which gives up a electron, which is picked up by the chlorine/bleach, which is thus converted to chloride. Chlorine also reacts with water to be converted into chloride, Cl-

(1) Cl2 + H2O ----> OCl- + 2H+ + Cl-

(2) ClO- (bleach) + C* ----> Cl- + CO*

And as Jon shows acetate produces has no + ions.

Chloride ions are not linked with anything once in water. They are separated from one another.

CaCL2 in water ---> Ca++ + 2 Cl2. The Ca++ gets used up and the Cl- does not. So you have Ca++ floating around by itself and Cl- floating around by itself attached to nothing

E.J. Coral

New member

Charge balance must be mantained through any chemical process, no exception. So while Ca2+ is absorbed by calcifying organisms another 2+ charge must be produced for every Ca2+ which is used. The produced species need not be closely asociated with the 2Cl-, but the overall charge of the solution must be 0. I don't know enough about biochemistry to tell what species is produced ... you can find the answer in a biochem text....


Bomb Technician (EOD)
Premium Member
This will help with what EJ is talking about. Charge Balance is a very large compliated subject. Here is a short intro on seawater and its CO2 carbonate systesm and charge balance 218-Lecture12.ppt

In a shorter text
Carbon dioxide, like other gases, is soluble in water. However, unlike many other gases (oxygen for instance), it reacts with water and forms a balance of several ionic and non-ionic species (collectively known as dissolved inorganic carbon, or DIC). These are dissolved free carbon dioxide (CO2 (aq)), carbonic acid (H2CO3), bicarbonate (HCO3-) and carbonate (CO32-), and they interact with water as follows :
CO2 (aq) + H2O H2CO3 HCO3- + H+ CO32- + 2 H+

The balance of these carbonate species (which ultimately affects the solubility of carbon dioxide), is dependent on factors such as pH. In seawater this is regulated by the charge balance of a number of positive (e.g. Na+, K+, Mg2+, Ca2+) and negative (e.g. CO32- itself, Cl-, SO42-, Br-) ions. Normally, the balance of these species leaves a net positive charge. With respect to the carbonate system, this excess positive charge shifts the balance of carbonate species towards negative ions to compensate. The result of which is a reduced concentration of the free carbon dioxide and carbonic acid species, which in turn leads to an oceanic uptake of carbon dioxide from the atmosphere to restore balance. Thus, the greater the positive charge imbalance, the greater the solubility of carbon dioxide. In carbonate chemistry terms, this imbalance is referred to as alkalinity.

In terms of measurement, four basic parameters are of key importance: Total inorganic carbon (TIC, TCO2 or CT) , Total alkalinity (TALK or AT), pH, and pCO2. Measuring any two of these parameters allows for the determination of a wide range of pH-dependent species (including the above mentioned species). This balance can be changed by a number of processes. For example, the air-sea flux of CO2, the dissolution/precipitation of CaCO3, or biological activity such as photosynthesis/respiration. Each of these has different effects on each of the four basic parameters, and together they exert strong influences on global cycles. It is important to note, the net and local charge of the oceans remains neutral during any chemical process.