The DPD testing

The DPD testing

Water treatment in pools. The DPD testing.

Dosing chlorine correctly is a key factor in water treatment in pools. Let’s have a look at the world’s most common method.

The DPD testing is one of the most common methods for measuring chlorine levels. The acronym DPD stands for N,N-diethyl-p-phenylenediamine. This method was first introduced by Dr. Palin, a German chemist, in 1957. It’s a simple procedure where we measure the colour depth of the reaction between the chlorine and the DPD reagent.

The use of chlorine in swimming pool disinfection is very usual and pool keepers need to control it very carefully in order to prevent infections while minimising eye irritation. How to make it possible? By keeping the combined chlorine residual as low as possible. No clue what I am talking about? Let’s take it step by step.

First of all, there are different types of chlorine present in pools. Swimming pool water generally contains three types of chlorine known as free chlorine, combined chlorine and total chlorine. You get the total chlorine by adding the free chlorine to the combined chlorine.

    • Free chlorine is the chlorine that is still available to disinfect your pool water.

    • Combined chlorine is the chlorine that has already been used to disinfect the water. It is thus combined with organic matter and responsible for the annoying smell of chlorine.

    • The total chlorine is the sum of the two.

Once the free chlorine has joined with microorganisms, its ability to disinfect decreases. Actually 25 parts of Combined Chlorine are needed to do the sanitising work of one part of Free Chlorine. The Total Chlorine level must be higher than the Free Chlorine level.

With the help of a DPD test kit in the form of tablets or drops, you can measure the pH, free chlorine and total chlorine levels by comparing the resulting pink colour with a colour scale.

Is the DPD method an effective way of controlling the water quality?

The DPD testing is indeed an effective method in order to measure the chlorine level in our pool. The only problem is that DPD not only reacts with chlorine but also with other oxidizing agents such as bromine, iodine or ozone. Its levels in private pools are though almost non-significant.

There are a few issues that you could come up with when reading the chlorine levels:

    • Unclear water can result in a darker colour

    • A dirty cuvette

    • A wrong calibration of the photometer

    • Expired test reagent

In order to avoid misleading measurements, it is important to get a large enough sample. We recommend to take at least 5 different samples, reject the highest and the lowest one and calculate the median of the 3 remaining values.

Follow these simple steps in order to keep your pool disinfection under control and enjoy your bathing season without eye irritation.

How to clean the pool after winter

How to clean the pool after winter

How to clean the pool after winter


Spring has finally arrived ! Days start getting longer and temperatures are more pleasant. Warm weather will soon be here. 


We look forward to buying sunscreen and to looking for our swimmsuit in the wardrobe. The first thing that we have to do before we can go bathing is to clean the pool after winter. We have to start thinking about getting our pool ready for summer when the outdoor temperature is about 20°C (68 °F). 

Another hint for timing the spring cleaning of your pool is when the water temperature is around 12°C (54 °F).  It depends on how sensitive to cold you are, but generally speaking, it’s then that it’s time to get the pool in operation again.

In case you don’t have time or you just don’t feel like doing it on your own, you can always commission a pool professional to clean the pool after winter. Pool professionals are either pool builders or gardeners with knowledge of swimming pools. Otherwise simply ask at your swimming pool supply store where you buy the pool chemicals and accessories. The last mentioned can clean your pool after winter for you or just give you some advice on how to do it because it’s quite easy.

When is my pool ready for swimming?

As aforementioned it’s time to get your pool ready for swimming when water reaches 12 °C (54 °F).

The pool needs to be prepared for winter when the water temperature is below 12 °C (54 °F). And at all events before freezing weather starts. The main steps are lowering the water level in the pool and shocking the pool with chlorine (chlorine level up to 0.8 mg/l). The filter system should run as long as possible. Afterwards remove the equipment from the pool and keep it in a dry place. Finally cover the pool with a winter cover.

If you prepared your pool for the hibernation correctly, then you’ll have to work less in spring in order to get it ready for summer.

You shouldn’t use your swimming pool during the hibernation. Even if the water level is below the skimmer level, the water quality isn’t safe for swimming. Never empty your pool during winter because it will prevent the foundation from getting damaged. Apart from this, water will protect your RENOLIT ALKORPLAN pool lining.

Steps to clean the pool after winter

1. Remove the winter cover

First of all remove the winter cover. Clean it by using a garden hose, let it dry and store it away in a dry place until the swim season is over. If you didn’t use a cover during winter, then the water will definitely be very dirty and you’ll have to clean the waterline properly.

2. Assemble the pool enclosure or pool blind

If you have a pool enclosure or a pool blind, now it’s time to clean it and to assemble it.

3. Completely drain the pool

This question always throws up controversy because many pool owners replace the pool water every 2 to 3 years. Water is after all a precious resource. Nonetheless, we recommend replacing the pool water after winter for hygiene and in order to spring-clean the pool liner.

4. Spring-clean the pool

Clean it immediately after draining it so that the dirt on the lining doesn’t get dry. With the aid of a garden hose gently scrub the walls. But not too vigorously, so that the reinforced pool membrane doesn’t get damaged. Lastly, rinse off with clear water.

5. Do not spray any pool algaecide

If any, only without copper. Elevated copper levels in water often cause discoloration on the lining.

6. Inspect the lighting, seals and filter
7. Fill the pool with fresh water

Close the drain valves (not the skimmer ones) and fill the pool with fresh water to the middle of the skimmer opening.

8. Turn the filter pump on

Clean the filter pump and turn it on when the water level has reached the middle of the skimmer.

9. Check the pH level

Check the pH level so that the pool chemicals perform in an optimal way. It should be around 7.2 -7.6. Use pH Minus or Plus to adjust the pH level.

10. Add the pool care products

In case you didn’t replace the pool water completely, it’s advisable to shock the pool to keep your chlorine level up and prevent algae growth.

That was it for „spring-cleaning the pool“. It wasn’t that bad after all, was it? So now your RENOLIT RENOLIT ALKORPLAN pool is ready for the summer. Download the checklist so that you don’t forget any important step before the swimming season starts. We wish you lots of swimming fun!