There are two main culprits to having irritated eyes in a swimming pool. The first is an outrageous PH. The second is too much chloramine in the water.
Chloramine is not chlorine in its free form. This is a disinfection byproduct and should be removed.
Hypochlorous acid, which is the effective agent in most pools will not have a noticeable chlorinated smell in the water, however if you have high levels of chloramine you may notice an odor in your swimming pool.
In general it is worth while to purchase a decent swimming pool test kit even if you hire a chemical company as it will allow you to check their work.
If your combined chlorine is above .5 ppm it may be time to consider BPC (Break Point Chlorination)
To begin it is recommended you test your pool water. You should test for free chlorine and total chlorine. To find the amount of combined you take the total chlorine and subtract the amount of free chlorine. The difference will yield your combined chlorine level.
Once you have the figure for combined chlorine you need to raise the free chlorine to ten times that value. For instance if you have a free chlorine value of 2ppm and a combine chlorine value of 1ppm you need to raise your free chlorine to a value of 20. This would mean that you need to increase your free chlorine by 18ppm.
One of the most common chemicals to do this is cal-hypo. Dosing this chemical does raise your ph and calcium levels in your pool. This is something to keep in mind. It is also why we recommend testing your pool chemicals prior to beginning this process.
Cal Hypo Dosing
To determine how much you need to add it is important you know the volume of your pool. Calcium Hypochlorite at 67% will raise your free chlorine level by 1ppm if 2oz is used in a 10,000 gallon pool. If you pool is half that size at 5,000 gallons then 1oz will raise your free chlorine by 1ppm. Dose according to your needs.
A reaction will happen between your elevated free chlorine and your chloramine that off gasses the resulting product. That being said make sure you do this with the pool cover off so the gasses have somewhere to go. If you are running an indoor pool carpet fans blowing air outside and open doors help. You need to let your pool gas off.
Additionally it is sometimes easier to do this at night as the cal hypo isn’t CYA (cyuranic acid) stabilized. This is a good thing as you can have too much CYA so when large volumes of chlorine are needed to super-chlorinate you do not want it to be stabilized. This will cause issues when you are returning the values back within normal range. Also this will hinder the process of UV removal.
Complication with Cal Hypo and other supperchlorination products
Bear in mind that cal hypo increases PH, total dissolved solids and calcium. While the PH affects are easy to overcome, the increased calcium and total dissolved solids can only be removed by partially draining your pool and filling it. If your pool uses a solar heater sometimes they have a limit on TDS for warranty purposes.
Sodium Hypocrite can be useful for dosing as well due to its low cost. Additionally if you already have a high calcium level it can be an alternative as it wont raise your calcium hardness. However the sodium in the sodium hypochlorite will raise your TDS levels.
Wait until the chlorine levels get back to an acceptable range. Typically around 3ppm. The chlorine will get degraded in the sun. With the sun out it should remove about 90% of that chlorine in just a few hours. If your worried test the water before getting back in. Just be sure that you dilute the swimming pool water if you are reading no chlorine as the levels can sometimes be so high that it bleaches out the dye used to test for it