For whatever reason, you have decided not to open the pool this year. Now it is mid summer and the pool water has turned green and you probably have this dark "stuff" on the bottom of the pool. If you haven’t already figured this out, you have an algae problem.
Algae can form in any pool, even one in operation, if proper chemical levels are not maintained. Algae growth can be exasperated in a closed pool by, of all things, a pool cover. By allowing light into the pool and holding in the heat, a pool cover left on the pool for a prolonged period can create the perfect environment for algae growth. Finally, lack of water movement in a closed pool can also help to hasten algae growth.
Algae growth in a pool may not be confined strictly to the pool itself. If algae is present in the pool, it is probably also growing throughout the system, including the skimmer, hoses and the pump and filter system.
Once the algae problem begins in a closed pool, there is no simple answer or magic pill to resolve the issue. The best option is to take proper preventative action when closing the pool. I will cover proper pool closing in a moment. But first lets address the problem at hand, which is removal of the green algae in the water and the dark algae growth on the pool floor.
As I said, there is no quick easy fix. The pool simply must be cleaned to eradicate the algae. First, you will need to add water in the pool to its normal operating level. Next, fire up the pump and filter system and conduct a thorough backwash of the system. This will loosen up any algae living in there. After backwashing, add a dose of algaecide to the pool. Algaecide can be purchased at any pool supply. This product will kill the algae and clump it so it can easily be removed. You will notice that a day after administering the algaecide, the water will be murky buy not green.
After the algaecide has dispatched the algae, you will now need to vacuum the pool. All of the algae that was killed with the algaecide will have settled to the bottom of the pool. Vacuuming should be a bit easier as the dead algae will be bunched in the center of the pool from the water rotation of the pump running.
If the algae growth on the bottom of the pool is excessive, it may be necessary to actually scrub the pool floor to remove the material. If this is required, use a soft bristled brush on a pole and gently scrub the pool floor. Then vacuum the pool again. This step may need to be repeated a couple of times to ensure all the algae has been removed from the pool floor.
Once the algae have been removed from the pool, I would recommend changing the sand in the filter. This will help to make sure that new algae growth is minimized. Now you should broadcast a “Shock” treatment onto the pool surface and continue to run the pool pump system for another day. You may now cover the pool and shut it down. Do not drain water from the pool. Leave water levels at normal operating levels, as you will need to run the pump and filter system periodically to prevent re-growth of algae. I recommend running the system once every week or two for a couple of hours. If the water starts to get a little green, add some more algaecide to the water when running the pump and filter system. A once a month broadcast of “Shock” will also help to minimize algae growth in a closed pool.
The best way to prevent a big problem with algae growth in a closed pool is to prepare the pool properly. Winterizing a pool will prevent damage to the system during those cold winter days, but does nothing for your pool once those warm summer days arrive.
To prepare a pool for a summer that you don’t intend on using your pool, you will need to take actions specific to this situation. First, refill the pool to normal operating levels. Start up your pool pump and filter system. Vacuum any debris that may have collected on the pool floor. Check the water and add chemicals accordingly to bring alkalinity and Ph to normal operating levels. Chemical levels will not need to be maintained for the summer, but it’s a good idea to have the chemical at operating levels up front.
The pool should be operated in this state for a couple of days. Next, shut off the pump and filter system and cover the pool. I suggest covering the pool with a heavy tarp that allows a minimum of light through and onto the water.
Now, every week or two, pull back the tarp, startup the pump and filter system and run it for a couple of hours, making sure to back wash the filter each time you start it up. If the water gets a greenish tint, add some algaecide to the water when running the pump and filter system.
When the temperature starts dropping in the fall and it is time to winterize your pool, follow your manufacturers instructions on how to prepare your pool for winter.
Even when a pool is not in use, it will still require some maintenance. Simply leaving a pool unattended is inviting bigger problems in the future. In addition to algae growth, a closed and unattended pool can provide a perfect environment for mosquitoes. Algae growth itself can cause damage to the pool liner over time, requiring replacement.
So, even if you are not intending to use your pool this summer, keep up with it. If you won’t be around to conduct proper maintenance, show someone how the system operates and have them do it for you in your absence.
See my other pool articles:
Backyard Pool Troubleshooting
Guide to Winterizing an Above Ground Pool
Pool landscaping, lighting and security
Proper Pool Chemical Balance
Understanding Above Ground Pool Pump and Filter System
Installing an Above Ground Pool