When it comes to shocking your swimming pool, one common question that leaves many homeowners uncertain is whether to recirculate or filter the water during the process. Pool shocking is essential for eliminating bacteria, algae, and organic contaminants, especially after heavy usage, storms, or signs of water cloudiness. But how your pump and filtration system is set during shocking can make a noticeable difference in the overall effectiveness of the treatment. Understanding the difference between recirculate and filter settings can help ensure your shock treatment works efficiently, saving both time and chemical costs.
Understanding Pool Shock and Its Purpose
What Is Pool Shock?
Pool shock refers to the process of adding a high dose of chlorine or non-chlorine oxidizer to your pool to destroy contaminants. This intensive sanitizing treatment is often needed after:
- Heavy pool use by swimmers
- Rainstorms or windblown debris
- Algae blooms or murky water
- Strong chlorine odors or eye irritation
The objective is to quickly raise the free chlorine level to oxidize harmful substances and restore water clarity and hygiene.
Types of Pool Shock
Different types of pool shock products are available, including calcium hypochlorite (cal hypo), dichlor, lithium hypochlorite, and potassium monopersulfate (non-chlorine shock). The specific product used can influence how your filter system should operate during application.
What Is the Recirculate Setting?
How Recirculate Works
On a multiport valve, the recirculate setting bypasses the pool filter and simply moves water through the pump and returns it to the pool. It creates strong circulation but does not trap any ptopics in the filter media. This setting is commonly used when the filter is clogged, or you don’t want debris to enter the filter system.
Benefits of Using Recirculate When Shocking
Some situations call for using the recirculate setting during pool shocking, such as:
- Preventing clogging of an already full or damaged filter
- Spreading shock chemicals evenly and rapidly throughout the pool
- Using powdered or granular shock that may leave residue
Recirculation helps disperse the shock treatment more quickly, especially in large pools or when water has not been circulating properly.
What Is the Filter Setting?
How Filter Mode Functions
The filter setting is the standard mode for daily operation, pulling water from the pool through the pump, passing it through the filter media (sand, cartridge, or DE), and returning it clean to the pool. It removes debris, ptopics, and some contaminants from the water.
Advantages of Filtering During Shocking
Using the filter mode while shocking is common and beneficial under normal circumstances. This setting:
- Continues cleaning the water by removing suspended ptopics
- Helps eliminate dead algae and oxidized contaminants after shocking
- Maintains consistent water flow across the entire pool
If your filter is in good condition and recently backwashed or cleaned, keeping it on filter mode can help improve overall sanitation results.
Recirculate vs. Filter: Which Should You Use When Shocking?
Consider the Condition of the Pool
To decide whether to recirculate or filter, consider the pool’s current state:
- If the water is extremely cloudy or contains visible debris, recirculate may be better to avoid filter clogging.
- If the water is mostly clear and the filter is clean, filter mode is typically more effective.
When to Use Recirculate
Choose the recirculate setting during shocking if:
- The pool has heavy algae that could clog the filter
- You are using a granular shock and want faster dispersion
- Your filter needs maintenance or is currently malfunctioning
When to Use Filter
Use the filter setting if:
- The pool is being shocked as part of regular maintenance
- The water is clear or slightly dull, but not full of debris
- You want to begin clearing up dead algae or organic contaminants
Steps for Shocking the Pool
1. Test and Balance Water
Before adding shock, test the pool water for pH, chlorine, and alkalinity levels. Aim for a pH of 7.27.4 to ensure the shock treatment is effective.
2. Choose the Right Shock Type
Select a shock treatment appropriate for your pool type and needs. Chlorine-based shock is good for heavy cleaning, while non-chlorine shock is ideal for regular maintenance without raising chlorine levels too high.
3. Set Pump to Appropriate Mode
Depending on the conditions described above, choose either the recirculate or filter setting on your pump’s multiport valve before adding shock.
4. Add Shock in the Evening
Shocking at dusk or night prevents UV rays from burning off chlorine, giving it more time to sanitize the water effectively.
5. Let Pump Run for 812 Hours
Allow your pump to circulate or filter water continuously for 812 hours after adding the shock to distribute chemicals fully and begin clearing out contaminants.
6. Clean the Filter
If using the filter setting, backwash or rinse the filter system after shocking to remove trapped debris and dead algae.
7. Retest Before Swimming
Check chlorine levels before allowing anyone to swim. Free chlorine should drop below 3 ppm for safe swimming conditions.
Tips for Maximizing Shock Efficiency
- Always pre-dissolve granular shock in a bucket before adding it to the pool to avoid bleaching the liner or pool surface.
- Remove pool toys and accessories before shocking to avoid chemical damage.
- Use a pool brush to agitate stubborn areas with algae before shocking.
- If using recirculate, plan to switch back to filter mode once shock treatment is complete to begin physical filtration.
Common Mistakes to Avoid
- Shocking during the day under direct sunlight, which reduces chlorine effectiveness
- Failing to adjust pH before shocking, which can reduce sanitizing power
- Leaving the filter off entirely during shocking, leading to poor circulation and chemical distribution
- Allowing swimmers back in the pool too soon after shocking
Whether to recirculate or filter when shocking your pool depends on several factors including the water’s clarity, filter condition, and type of shock used. In general, recirculate mode is ideal for quickly spreading chemicals without clogging the filter, especially when dealing with algae or heavy debris. Filter mode, on the other hand, is best for clearing contaminants and maintaining water quality after the initial shock treatment. Understanding how and when to use each setting will ensure your pool stays clean, safe, and enjoyable all season long.