Pool Shock: Shocking for Algae Removal


Welcome back to school, students! August is the perfect time to discuss algae, and how to remove it by shocking the pool with Calcium Hypochlorite – Ca(OCl)2.

Chlorine is a Great Algaecide, I like to say. Faster kill rates, and a more complete reaction than using algaecide, or other oxidizers.

Cal Hypo is the perfect chlorine type to use as pool shock – powerful and economical.

Our discussion will focus on how much pool shock to use for a complete algae removal treatment, plus other tips on effective pool shocking.

Preparation for Shocking

1. Clean Pool Thoroughly. If your pool has debris or leaves on the bottom or floating on top, this will interfere with the process. Chlorine will attack this organic matter, rather than the algae.

If the pool is too dark green to see the bottom, use a Leaf Rake, or the Leaf Gulper and clean 98% of the debris from the pool before shocking the pool.

2. Lower the pH. Cal Hypo (and in fact all chlorine products) have greater efficacy at a lower pH level. Add an acid to adjust the pH to 7.2. Check your Alkalinity first, to make sure that it’s in the range of 80-120 ppm, before adjusting your pH level.

3. Assess the Algae. Determine the level of severity of this algae attack. Is this a summer bloom that was caught early, or has the pool sat neglected for months? Choose one of the three icons below to indicate the level of algae in your pool.


LIGHT GREEN: Water is mostly clear, with areas of visible algae.
MEDIUM GREEN: Algae in all areas, visibility low at 18-36 inches deep.
DARK GREEN: Thick algae deposits, visibility limited to 12 inches deep.

Shocking for Algae Removal

It’s a generally accepted notion that 30 ppm of chlorine residual will kill all algae. Assuming that your pool is clean, and you have adjusted the pH, you can now add the granular chlorine to the pool.

Most pool shock packages will list directions to add 1 lb. (1 bag) of shock per 10,000 gallons of pool water. That may be fine for normal conditions, but if you have a severe algae attack, more will be needed.

“Shock it until the water turns Blue-ish”, said one of our pool guys on staff here. “That’s what I do”. Not a bad technique – you do want to add shock to the pool until the water loses the green color, and turns a blue-gray color.


Here’s a chart that can be used with our Pool Shock and Super Pool Shock products. The numbers indicate the amount of shock, in pounds. You may need more to see the blue color begin to return to the pool.

5 Tips for More Effective Algae Removal

  1. Don’t use an algaecide before shocking, pool shock will break apart the polymer chains, rendering it useless.
  2. Check your pH, before shocking, and then again a few hours after shocking.
  3. Dilute your chlorine in a bucket for vinyl pools; for plaster pools, just pour it in.
  4. Run the filter 24/7 until water is clear. Backwash only as needed.
  5. Brush the pool vigorously, after shocking the pool.

Cleaning Up

After a few days, you can vacuum up the shock dust, or brush it daily and run the pool cleaner if you don’t have a way to manually vacuum the pool.

Brushing is an important step, immediately after shocking, and for a few days afterwards. Use a good quality pool brush for the best results.

pool brush

Using a pool filter cleaner after a major clean-up is a good idea. Depending on the age, you may also elect to change the filter media, with new sand or a filter cartridge replacement.

Once you have things under control, you can begin using maintenance doses of a good quality algaecide, maintain a constant chlorine level, and operate the filter for 12 hrs +/- daily.

In Sum, shocking for algae removal requires a good pH, a good brush, and a good dose of Cal Hypo pool shock, available in bags and buckets.

Keep America Blue!



Dr. Pool


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