Green pool water is almost always due to algae, although excess copper from an ionizer or flow-driven metal sanitizer (such as Nature2) can turn it a light greenish color. Once algae begins to grow in a pool, it quickly overwhelms the system, turning from light green to increasingly darker shades of darkness. Algae can double every 12 hours or less, depending on conditions. The pool quickly becomes unusable, and not just for cosmetic reasons. Algae can harbor unhealthy levels of infectious bacteria.
Algae can have several causes, but the main one is an inadequate disinfectant. In most pools that use chlorine as the primary sanitizer (including pools that use salt-based chlorine generators), this means that there is not enough Free Available Chlorine (FAC) in the water. For most pools this would be 2-3 ppm, assuming “balanced” pool water.
What can you do with algae?
An ounce of prevention is worth a pound of cure. Pool algae is a perfect example of one of Ben Franklin’s most famous aphorisms. As you’ll see below, getting rid of algae once it’s established in your pool is an onerous process. You should avoid algae formation if possible. There are two solutions for algae, the first based on prevention, and the second based on the cure.
Prevention: Keeping the water clean prevents algae
Preventing algae from forming is much easier than cleaning up after it sets in. Basically, you have to keep your water clean and well sanitized continuously, and algae won’t form. However, if you’re sanitizing your pool with traditional chemicals, this can be a lot of work in itself, with ever-changing chlorine, stabilizer, algaecide, pH balancers, and other chemicals.
We suggest a simpler alternative (assuming you start with clean water):
- Install an ozone generator in the water circulation line downstream of the pump according to the manufacturer’s instructions. DEL Ozone offers pool ozonators for all sizes of residential pools.
- Keep Free Available Chlorine (FAC) at a level of 0.5 to 1.0 ppm to continuously circulate in the pool (heavy bathers may require more).
- Test often at first for pH (balance should be 7.2-7.6 – add an acid like muriatic acid or alkali like soda ash to achieve this) and chlorine (add as needed). With experience, you’ll learn how often and how much chlorine to add, partly determined by how you use the pool.
Enjoy your pool!
Cure: get rid of algae
Once the algae takes hold, a chemical attack is required to remove it. The ozone generator cannot remove high concentrations of algae growing in the pool (especially organisms attached to the pool walls) because most of the ozone is destroyed in the disinfection process before the circulating water reaches to the pool. Only a small residual level of ozone remains at that point, usually not enough to penetrate the nooks and crannies of the pool; that’s what the background FAC is supposed to do.
Here’s what to do to get rid of algae:
- Adjust the pH to the normal range, 7.2 to 7.6.
- Brush the walls and bottom of the pool to loosen attached algae.
- Make sure the pool filter is clean and turn on the pump. Keep it running throughout the process.
- Shock the pool with a chlorine-based product. This may require 2-3 times the normal amount of flushing; read the product instructions.
- Add an algaecide along with the shock. Some algaecides are meant to be used in conjunction with shock, and some are not compatible with chlorine or ozone and may stain the pool, so read the label carefully.
- Test and check the water, repeating the shock process every 12 to 24 hours until all algae are dead and discolored.
- Although dead algae will begin to settle to the bottom of the pool, adding a flocculant (floc treatment) will help the algae particles coagulate, making cleaning and/or filtration more effective.
- Vacuum the pool and check the filter. Clean the filter if possible, but this algae-killing cure often overwhelms the filter, so replacing it may be the best option.
- Include an algaecide in your chemical routine and shock treat the pool once or twice a month to prevent future algae blooms.
Enjoy your pool!
Avoid the cure: install an ozonator
If you’d rather swim in your pool than clean it, find the right pool ozonator for your pool, clean the water once, then maintain it with ozone and an appropriate amount of background chlorine. One benefit of this method is that your pool water will be and feel fresher with fewer chemicals, and you will also avoid problems with harmful chlorine byproducts like chloramines.
Maximize the power of ozone
It is important to note that ozone is injected into the pump flow and only when the pump is running. For proper sanitation and disinfection, DEL Ozone, the world’s leading innovator in ozone sanitation applications, recommends running the main pump at least 6 hours per day, depending on the recirculation (rotation) rate of the pool.
However, the pool ozonator could be running 24 hours a day for maximum sanitation and disinfection power. With today’s energy saving variable speed pumps often required for in-ground pools due to power requirements, this can be a limitation because most manufacturers’ ozone generators run only at high speed. Fortunately, DEL Ozone offers a variable speed injector manifold that will work at any pump speed, so both energy savings and maximum pool ozone efficiency can be achieved.
Enjoy the pool more!