Solution vs. Suspension

Solution vs. Suspension (or "why does my pool turn cloudy when I shock it?")

If you have ever see a pool get really cloudy after shocking, then this section is for you. 

When you put a chemical into the pool, it can do one of two things:

1.  It gets dissolved and goes into solution in the water. 

2.  It cannot be dissolved and goes into suspension in the water. 

What determines whether something goes into solution or suspension?

The saturation level of the water is what determines its ability to dissolve materials.  If water is already highly saturated, then it will have a hard time absorbing more alkaline material.  In other words, if you have a high alkalinity reading, and then shock the pool with a high pH material like Calcium Hypochlorite (pH 11.3), the chlorine will go into the water and will sanitize just like it needs to, but the water will not be able to absorb the high pH base material that makes up 35% of the Calcium Hypochlorite.

When you find a cloudy pool, it is important to do a full chemical test, especially the chlorine, pH and Alkalinity. 

To understand the concept of solution vs. suspension, take a glass of water and pour a teaspoon of salt into it and stir it up.  Pretty soon the salt "disappears" because it is being dissolved into the water.  It has gone into solution.  Keep adding salt and stirring and pretty soon, you will find that the salt will no longer dissolve easily into the water.   In fact it settles to the bottom and if you stirred it up, you would see the undissolved salt suspended in the water.

If the water is not highly saturated, then alkaline materials will dissolve rather quickly into the water.  If the water is over saturated, then the alkaline materials may take a long time to dissolve into the water.  On a pool with a really low pH or alkalinity, soda ash will dissolve very quickly and chlorine shock will not cloud up the water.  If the pool has a high pH or alkalinity, the soda ash will create a cloud in the water that may take several hours to go away.  The same cloudiness can be seen by adding Calcium Hypochlorite to a pool with a high pH or alkalinity.