Pool Plant Courses - Blog

Sometimes there will arise a need to introduce chemicals into the pool manually (hand-dosing). This is a potential hazardous activity and should not be performed by people who have not received the appropriate level of training.

General Procedures

• Always wear the appropriate PPE.

• Always add the chemical to the water, NEVER add water to the chemical.

• NEVER mix a chemical with another chemical. Only ever mix with water.

• Never hand-dose chemicals into the swimming pool when occupied.

• Always allow time for thorough mixing and distribution of the chemical into all areas of the swimming pool water.

Increasing Chlorine

The following method will outline how to add a hypochlorite disinfectant to the swimming pool. If you’re using a chlorinated isocyanurate disinfectant, follow the manufacturers’ instructions as the method will be different.

We recommend using calcium hypochlorite granules for the purpose of hand-dosing. It’s safer to store and handle than sodium hypochlorite.

Step 1. The first thing you need to do is calculate how many cubic metres of water you have in your swimming pool. Do this by multiplying the length by the width by the average depth. See the worked example below:

Length (20m) X Width (10m) X Average Depth (1.5m) = 300m3

Step 2. The next thing to do is calculate how much calcium hypochlorite granules you need to add in order to increase the free chlorine reading by 1mg/l. Do this by dividing the pool volume figure (from step 1.) by 0.65. The reason you need to divide by 0.65 is because calcium hypochlorite is typically only 65% chlorine. Some products are 70% chlorine, in which case you would divide by 0.70. See the worked example below:

300m3 / 0.65 = 462

The figure obtained provides you with the amount of grams of calcium hypochlorite granules you need to add to the swimming pool in order to increase the free chlorine reading by 1.00mg/l.

Step 3. Use a set of kitchen scales to measure out 462g of calcium hypochlorite granules into a clear plastic jug.

Mark a clear line on the jug to indicate the level of calcium hypochlorite granules at 462g.

Step 4. Decide how much you need to increase the free chlorine reading by. For example, if you have zero free chlorine in the pool and you would normally operate at 2.00mg/l, then you need to increase by 2.00mg/l. This equates to the number of jugs of calcium hypochlorite granules you need to add to the swimming pool, i.e. 2 jugs.

Step 5. Now you need to add the granules to the swimming pool water. This can be done by carefully depositing the granules into either the overflow channel (in a deck-level pool) or the skimmer baskets (in a skimmer-basket pool). From here, the granules will be drawn into the balance tank (if there is one), or directly into the suction-side pipework of the circulation system. 

Step 6. Allow some time for the granules to dissolve and make their way around the system and into all areas of the swimming pool. How long this will take will be dependent on a number of factors, such as the efficiency of the system hydraulics.

Step 7. Carry out a set of pool tests, taking the sample from a point in the swimming pool as far as possible from the inlets. This is to help you determine whether the chlorine you have introduced has been distributed to all areas of the swimming pool. If necessary, carry out further tests in order to be sure that all areas of the swimming pool have a sufficient level of disinfectant. Once you are satisfied of this, you can open the pool again to bathers.