Winterising guide for pools with a salt chlorinator

Which option suits you

Good winterising stops the water turning green over the winter and saves you work and product in spring. The first thing to decide is whether your pool will keep filtering during the winter or be shut down completely.

In southern Spain and on the coast, active winterising is the usual choice.

Before you start: common steps

These steps are done when you close the season, while the water is still in good condition, whichever option you choose.

1. Test the water. Adjust the pH to 7.2–7.6, which is the range in which winterisers work. Also measure the salt with salt test strips: don’t work it out from the salt you have been adding, because salt is lost with filter backwashes and water top-ups.
2. Clean the pool. Floor, walls and waterline. Empty the skimmer baskets (the suction openings in the wall) and the pump pre-filter.
3. Backwash and rinse the filter. That way winter starts with clean sand.
4. Check the chlorinator cell. If you see a white layer on the plates, it is limescale: it reduces chlorine output and can trigger false low-salt warnings. Immerse the cell in a dedicated cell cleaner until the plates are covered, without going past the cap, and rinse it thoroughly with water. It is an acidic product: don’t leave it in longer than necessary, follow the time given in your chlorinator’s manual and wear gloves and goggles. Never scrape or brush the plates.
5. Shock chlorinate with shock chlorine, at a rate of 15 g per m³ of water.
6. The next day, add the winteriser with the filtration system running so that it spreads. Some liquid winterisers require free chlorine to have dropped below 0.5 mg/l before they are added: in that case, wait for it to drop. Always check the product label.

How to choose the winteriser

The winteriser is the product that keeps the water free of algae during the winter. To choose one, consider three things: your pool lining, whether it will keep filtering, and the volume of water.

1. The lining. Many winterisers contain copper, which is a good algaecide but stains and discolours liner, polyester and vinyl. If your pool has one of these linings, always use a copper-free winteriser. In concrete or mosaic-tiled pools both versions are suitable. Copper-containing winterisers are compatible with salt chlorinators.

2. Liquid or floater.

3. Pool size. Liquids are dosed according to the m³ of water, so they suit any pool. Floaters go in steps, usually one per 50 m³, and are adjusted by opening more or fewer holes. In small pools they can release too much chlorine: some manufacturers don’t allow them below 40 m³ or in raised above-ground pools. Large pools need several. The floater must always stay afloat, never resting on the floor or walls, because undissolved chlorine discolours the lining.

Option 1: active winterising

The filtration system keeps running for a few hours and the chlorinator rests. It is the most convenient option in frost-free areas.

1. Carry out the common steps in the previous section.
2. Adjust the chlorinator to the water temperature. With the water above 15 °C it can keep running with adjusted output. Below 15 °C we recommend switching the chlorinator off and leaving the work to the winteriser: if the cell runs continuously in cold water, its lifespan is shortened. If you prefer to keep it running, turn the output down to the minimum.
3. Reduce filtration. With the water below 16 °C, 1 hour a day is enough.
4. Don’t drain the filter. Backwash and rinse it every 30–60 days even if the pressure gauge doesn’t call for it, so the sand doesn’t compact.
5. Repeat the winteriser halfway through the winter, as indicated on its label. If you use a floater, replace it when it is used up.
6. Check the pool once a month: pH, water level above the skimmers, clean baskets and how the water looks.

In cold water it is normal for the chlorinator not to reach 100 % output or to show lower readings: salt conducts electricity less well at low temperatures. It is not a fault.

Option 2: full shutdown

The installation is shut down for months and protected from frost and damp.

1. Carry out the common steps, including the winteriser with the filtration running for a few hours to spread it. For this option there are liquid winterisers designed for leaving the filtration off all winter.
2. Switch off and remove the equipment. Disconnect the electrical panel and remove the chlorinator control unit, the pH controller and the pump motor. Store them somewhere dry: winter damp damages electronics and the motor.
3. Lower the water level below the skimmers.
4. Drain the filter. Once it has been backwashed and rinsed, drain it completely and leave the lid on but unscrewed so it can breathe. Close the valves, leave the drain open so the pipes and valves empty, and cover the filter with a tarpaulin or plastic sheet.
5. Leave the cell without water, in place and with its isolating valves open.
6. Always store pH and ORP probes wet, with their cap and storage solution. Never store them dry or in distilled water, as this damages them. If they will be stored for more than 3 months, check and calibrate them before using them again.
7. Cover the pool with its winter cover.

In spring and frequently asked questions

Before switching the chlorinator back on, check all of the following:

• Clean water with no algae (if there is algae, treat it before adding salt)
• pH between 7.0 and 7.2
• Water above 15 °C
• Free chlorine above 1.5 ppm, after a prior shock chlorination
• Salt measured with strips and adjusted to what your equipment requires (usually 5 kg per m³)
• 24 hours of filtration with the salt already added, so it dissolves
• Clean, calibrated probes; filter filled, backwashed and rinsed

My chlorinator produces little in winter. Is it faulty? No. In cold water salt conducts current less well and output drops. It is normal.

When I start it up it shows low salt. Measure the actual salt with strips before adding more, and check whether the cell has limescale on the plates: limescale causes false low-salt warnings.

Should I add salt in spring just in case? Better to measure first. Salt isn’t used up by electrolysis; it is lost mainly when topping up water and backwashing the filter.

Can I use a winteriser with copper in my liner pool? No: copper stains liner, polyester and vinyl. Use the copper-free version.

A plate in my cell has broken. Can I replace just that plate? Individual plates aren’t sold: the complete electrode is replaced.

Recommended products

Always follow the dose on each product’s label. If you are unsure which one suits your pool, tell us the volume and lining and we’ll help you choose.

For start-up and equipment care:

If you need help with your specific case, our technical support team is at your disposal at quimipool.com.