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Preventing a Green Pool Opening

If your pool opens up green every spring, this post is for you. Here's some ways to prevent a green pool opening, and be confident of a blue pool when the cover comes off. Pools open green when the winter cover is not keeping out debris, the water chemistry is poor, and there is inadequate sanitizer.

Even if you open late, and even if you have a mesh safety cover - you can skip the stains and discoloration by avoiding these problems with the pool cover and the winter water chemistry.

Install a Safety Cover

safety cover

One of the most guaranteed ways to prevent a green pool opening is to install a solid safety cover without drain panels. Safety covers keep out winter air pollution, pollen, and dust by blocking rain and snow. This helps keep the water balanced and conserves chemicals.

For pools with a raised wall, for a raised spa or higher deck level, there are two ways to install a safety cover: in the wall, or over the wall. In-the-wall installations may not fit so well, and fill with leaves during winter. It's always best to go up-and-over on pools with raised walls.

Floating solid pool covers, with water bags, can be a great cover when drained regularly and kept clean. However, they are sensitive and can tear if debris or animals scratch the surface. If you don't maintain the cover well, a large tear can develop and spill contaminated matter into your pool.

Maintain Winter Water Balance

Pool Magic + PHOSfree

If you close your pool clean, with balanced water, and a winter kit, you can expect those chemicals to last about 5 months.

For pools that open green each year, something extra is needed, like Pool Magic + PHOSfree. Pools with green spring openings usually have a phosphate problem, although they may also have cover problems and/or water level problems.

The most important thing to note with winter pool chemicals is that more will be needed if you have contaminants entering the pool, be they full sized leaves, or dust that washes off the trees. More will also be needed when the temperature of the water rises.

Pool Water Temperature Concerns

When the pool water temperature drops to 50ºF or below, the algae risk is almost nonexistent. Chemicals also last longer when the water is cold. But when the water temps warm up in the spring, your chemical protection can deplete quickly. In temperatures above 65ºF, winter pool chemicals become active and will work themselves to death.

Use winter chemicals just after closing and just before opening. During the colder months, very little is going on under the cover, but as things heat up, more chemicals are consumed, and more organisms spring to life. Mesh covers will allow some sunlight to pass through, which can warm the pool surface.

Mesh Pool Cover Problems

Solid and mesh covers with drain panels let in all sorts of microscopic debris during the winter. If the pool water level is allowed to touch the underside of the cover, leaves get stuck on the cover, and a tea bag effect is created.

Water balance can change dramatically in a mesh covered pool. It should be checked at some point during the spring. It's a good idea to add an extra dose of shock or algaecide (but not both) as the weather begins to warm up into the 60's.

Our Recommendation

In mid to late spring, or about a month before you plan to open the pool:

  1. Remove springs on both sides of the pool. Fold x onto itself in the center.
  2. Use a small submersible pump or a siphon to lower water below the tile.
  3. Check and balance the water chemistry and shock the pool, or add a Qt. of algaecide.
  4. Fill the chlorine floater with tablets.
  5. Brush the walls on both sides of the pool.
  6. Put the pool cover back on tightly.

If you open up to a green pool each spring, think if you have any of these problems above, fixing one or more of them can give you a beautiful blue pool next spring!

In The Swim makes every effort to provide accurate recommendations based upon current ANSI/APSP/ICC-5 2011 (R2022) standards, but codes and regulations change, and In The Swim assumes no liability for any omissions or errors in this article or the outcome of any project. You must always exercise reasonable caution, carefully read the label on all products, follow all product directions, follow any current codes and regulations that may apply, and consult with a licensed professional if in doubt about any procedures. In The Swim assumes no legal responsibility for your reliance or interpretation of the data contained herein, and makes no representations or warranties of any kind concerning the quality, safety, or suitability of the information, whether express or implied, including, without limitation, any implied warranties of merchantability or fitness for a particular purpose.