What, you want the cliffs notes version?
Ok, lets see here. There are 3 importan concepts in there. Fist; the solubility of simple solids, second; saturation and supersaturation, and third; precipitation.
A simple ionic solid (like calcium chloride) can dissolve in pure water. That means that the ions seperate in solution and are essentially suspended in the solution. They dissolve and seem to "dissappear" to us.
You can keep adding calcium chloride salts to a fixed volume of water up to a given point. Eventually, the water becomes stuffed full of ions and cant hold anymore. At that point, if you add more CaCl, it does not dissolve. It remains a solid salt. That concentration is the point of saturation. Saturation points change if multiple ions are added to a solution. So while pure water may be able to dissolve the equivalent of 2000ppm of CaCl only, when you start adding NaCl, CO3 (carbonate), 2CO3 (bicorbonate), Mg (magnesium), and other ions, the amount of CaCl it can hold diminishes.
A good analogy would be if you have a 5g bucket, you could fill it all with 5g worth of water, but what if you wanted to add other things like rocks, dirt, toys, etc? Then some of the water has to be removed to still have only 5g of capacity. Hope that makes sense
Along with saturation (the point at which water cannot hold anymore ions), is supersaturation. By using liquid additives it is possible to temporarily create a point of supersaturation of an ionic solid in water. In other words, the chemicals you dose are usually only the chemicals you dose. A very high concentration exhists in those bottles. When you pour them in they start mixing with your tank water which is allready nearly saturated. For a breif period, the water will be at a point beyond its saturation basically having more ions in the water than is possible. This is called supersaturation and is inherently unstable.
When a supersaturation exhists in solution, one of two things has to happen. Either the ion dissolves into the larger volume, or it precipitates out of solution and becomes solid again. Since our tanks are nearly saturated and a fixed volume, usually the only option is precipitation. In marine aquaria, when too much calcium is dosed and alkalinity and pH remain low-moderate you reach a point of supersaturation of calcium. Then the Ca++ ions have to become a solid again. They cannot become Ca2 (calcium salt) as this is highly unstable and explosive in water. Instead they bond with CO3-2 (bicarbonate) to create calcium carbonate (a white crusty salt). Unfortunately the reaction that combines Ca++ with CO3-2 will continue from the point of supersaturation, down to the point of saturation, and continue to well below the point of saturation as the reaction is favorable.
So when you add Only a CaCl additive, your momentary concentration of Ca++ jumps well up over 500-600ppm. This is chemically unstable and it binds with bicarbonate and crashes well below 300ppm. That crash causes your coraline to stress and become white. The resulting crash and temporarily low pH causes some of the CaCO3 that is created in the crash (but not all) to re-dissolve and bring your levels back up to around 350ppm/8dKH. This is a very common problem with beginner aquarists that only test for one element and not any of the other two. Maintaining a proper balance between calcium, alkalinity, and magnesium will greatly benefit your tank in the long run.
So where should you go from here? Start by slowly dosing bi-carbonate to bring your dKH up to around 10. Once there, start dosing calcium to bring that up to around 400ppm. Do not stop dosing bi-carbonate during this time scale as maintaining a stable alkalinity is required. If magnesium is way out of whack, go ahead and dose that, but its probably in the ballpark. Once you reach about 400/10 you can go for say 420/11, and probably a decent stable area for growing coraline is around 440/12. Attemt to keep Mg over 1250ppm during this process. Remember, this is of utmost imoprtance:
Never dose multiple chemicals simultaneously. Adding a calcium and a carbonate additive to the same tank at the same time is just asking for precipitation to occur. Wait at least 30 minutes between doses.
Hope that makes sense.
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