Total Alakalinity is to swimming pool water what the Liberal Democrats used to be to british politics. Over shadowed by the other two but important in their own way.
In swimming pool water chemistry the big two are pH and free chlorine level. You have to test for these on a regular basis to be sure your pool is safe and comfortable to swim in. In order to make the water comfortable for bathers eyes and to make the chlorine most effective you must keep the pH between 7.2 and 7.4. Altering the pH is done by adding pH reducer (Dry Acid) or pH increaser (Soda Ash). How easy it is to alter the pH by adding these chemicals is determined by the amount of Total Alkalinity in the water. The ideal range for Total Alkalinity is 80 to 120.
If your Total Alkalinity is too low, when you add pH increaser or pH reducer the pH will alter dramatically with the addition of a small amount of chemical. So your pH will swing from too low to too high or vice versa. If your Total Alkalinity is too high, when you add regular amounts of pH increaser or pH reducer the pH it will have no effect. You have to put much more chemical in before you notice any movement on the pH.
Imagine a traditional weighing scale balanced with equal weights on either side. You have a 10g weight to add to one side. If the weight already on each side is 10g then an extra 10g on one side will make a huge difference. This is like having low Total Alkalinity. If the weight on each side was 500g then adding 10g will hardly have any affect at all. This is like having high Total Alkalinity.
 Low Alkalinity. Adding 10g makes a big difference |
 High Alkalinity. Adding 10g makes no difference |
So if you are getting wild swings in your pH you need to increase the Total Alkalinity. This is easy, just add some Alkalinity increaser. You can see more on Alkalinity Increaser on the main website.
Lowering the Total Alkalinity is not quite so easy. You need to add acid (pH reducer) to the water but rather than spreading it evenly through the water you need concentrate it all in one spot. There are many ways to achieve this and we can’t recommend one method over another. If you know a good way tell us about it. One way is to mix up a bucket of water and dry acid and dump the whole lot in one go in to the deep end. We have tried putting 3kg of dry acid in a washing up bowl, putting it on the steps of the pool and leaving it for a few days. The pool water will gradually disolve the dry acid and bring the Total Alkalinity down. Another way is to take a whole 7kg container, puncture it with nail holes and dangle it in the pool until the Total Alkalinity is about right.
High Total Alkalinity is not a problem from the point of view having safe and comfortable water but lowering it will make life easier for you when adjusting your pH.