Swimming Pool Blog
by Rob Cox, May 21, 2012
Green Pool Opening
Pictured left is Charlie O's pool in southern New Jersey. We're not sure what happened during the winter, but last week's pool opening was more work than he expected.
Could have been that the water wasn't quite clean and clear before closing. Perhaps the closing chemicals weren't strong enough or just ... enough. Maybe phosphates have contaminated the pool, providing a rich food source for algae to grow fat and happy.
I first told Charlie - "You can see the bottom floor of the pool, so you should be able to bring it back. Lower the pH and shock it good - then run the filter 24/7". My standard answer; usually sufficient.
Charlie got back to me the next day with pictures of his DE filter being clogged with what he called "Green Slime". Indeed, these DE grids were very green, and this was sending the pressure gauge sky high, after just a few short hours of running the filter.
Frustrated, Charlie decided to drain the pool. He's done this before, when he painted the pool, so he was comfortable with using a small pump; hosing off the walls and floor as the water lowered.
Dropped a hose in the pool, and filled it back up in a few days. Balanced the water, started the filter, and sent me a proud picture of his newly blue pool.
How to bring back a green algae pool
1. Drain the Pool:
You could do what Charlie did, drain the pool - sometimes water is cheaper than chemicals. I'm of the belief that you can't really "waste" water - we have roughly the same amount of water on the planet as we did a thousand years ago. However, if you live in an area where drought has struck; parts of Arizona and Texas come to mind, draining the pool may not be feasible.
If you live in a rural area, where your water comes from a well, it can be slow to fill, and hard on the pump. Trucking in water from a pool filling company can get expensive, usually over $1000 to fill a pool. I heard a news story a few weeks back that some Texas water delivery companies were charging 4x that amount!
If you live in an area where water is fairly cheap and plentiful, however - draining the pool may be a good option. If you haven't replaced the water in 5+ years, you may be due for a change. Over time, your pool water can build up dissolved solids and other invisible matter that can consume more chemicals and make water management difficult.
To drain the pool properly, there are some important considerations to avoid complications.
a). Drain to the gutter, or to a storm drain. If this is not possible, make sure to pump at least 50 feet away from the pool. You should avoid pumping the water in an area where it will stand or "pool". Water that is pumped too closely to the pool can make its way quickly underneath the pool. This can cause problems for vinyl liners that "float" or bulge at the point where the water comes to rest under the liner. For concrete pools, the hydrostatic pressure can be so great in some cases, that it can actually pop the pool out of the ground.
For more information on safely and properly draining your pool, see an earlier blog post on how to safely drain a swimming pool.
b). For Concrete pools, be sure to open the hydrostatic relief valves that are plastered into the pool floor and in the main drain pot. These are small threaded caps that will allow the water beneath the pool to come into the pool, rather than push the pool up (which is rare).
c). For Vinyl Liner pools, drain only half of the pool, then fill up again. If you get too close to the floor of the pool, you take the risk that the liner will relax, and pull away from the wall. When this happens you will need to "reset" the liner, using a vac/blower. There is also a risk that while trying to reset the liner, some part of the vinyl could "give", if it is an especially old and brittle liner.
d). If your pool is especially green and messy, using a 5-8hp gas powered pump will be better than using a small submersible pump. Trash pumps, as they are sometimes called, they will suck up and spit out items as large as a golf ball. Secondly, you will want to pump the pool fast, so that you can keep up with hosing off the walls and floor as the water level drops. If you don't do this, the green muck will dry and stick to the walls, creating an even bigger mess, and more stains.
e). Using a pressure washer is suitable for concrete, but too much pressure on loose tile or loose plaster could create another job for you! Keep it under 3000 psi for concrete pools, and for vinyl pools, keep it under 2000 psi, and use care not to damage the liner. If you are using muriatic acid to acid wash the pool, use extreme care, as this is a fairly dangerous substance. See our earlier blog post on acid washing for more information.
2. Chemically Treat the Pool
Generally speaking, if you can see the bottom of the pool, you can bring it back with proper chemical levels, lots of chlorine and lots of filtering. You will need a good filter to pull this off - not one that is "marginal" or "adequate". Here's some tips on bringing back your pool through chemical management and good filtering.
a). Clean the pool very well. Every bit of organic debris in the pool will make the job more difficult. Use a leaf net (the bag type) to remove as much leaves and debris as you can, from the surface and the floor of the pool. You will not be able to bring back the pool if it is filled with debris. Vacuum to waste, if you have a multiport valve. The more debris and algae that is manually removed, the easier the job will be, and the more efficiently your chemicals will act.
b). Before shocking the pool, balance the water and lower the pH level. Adjust the Total Alkalinity level to between 80-120ppm, and the Calcium Hardness levels to 180-220ppm. Then lower the pH level to the 7.2 range. Your chlorine shock will be much more effective at a lower pH level, and - as an added benefit, algae hates a low pH level, but thrives at pH levels of 7.8 or higher.
C). Introduce enough chlorine to raise the chlorine level to 30ppm. This is difficult to test with a standard test kit, but it roughly equates to 2 lbs of shock per 10000 gallons. A rule of thumb I like to use is to keep shocking the pool until you see the water turn a blue/gray color - or until all of the green color has dissipated. If the green color returns in a day or two, repeat the process.
d). Run the filter 24/7 until the water clears. Backwash only when the pressure gauge rises 8-10 lbs above the clean, starting pressure.
e). Add a clarifier, following label directions, to assist in coagulating suspended particles.
f). Brush the pool very well, and then vacuum to waste again.
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