Cleaning up a swampy green pool is no walk in the park, it can take hard work balancing, cleaning and filtering the water to return a dark green pool to swimming condition.
And vinyl liner pools, they present a particular challenge. You've probably been told that it's best not to drain a vinyl pool, and you may be rightly concerned about using very harsh chemical treatments that could harm the pool liner. So, what's a vinyl liner pool owner to do?
Here's my recipe for turning around a dark green algae filled vinyl liner pool.
Step One: Clean the Pool
The first thing that has to be done is to clean the pool, to remove as much organic debris as possible. There's no way the water will come back if you have a layer of leaves on the bottom of the pool, or floating around on top. Cleaning should be done daily. Vacuuming, skimming and brushing the pool to remove accumulated dirt and algae from the walls and floor.
Vacuuming to Waste: If you have the ability to vacuum to waste (with a multiport valve), this will make the process easier. Roll out the backwash hose and put the multiport valve onto the Waste setting. Fill the pool up first, and keep a hose running while vacuuming if necessary, and vacuum fast - before the water level drops too much.
Cartridge filters are often plumbed without a way to vacuum to waste, unlike sand or DE filters that have a multiport valve. However, a handy homeowner could install a 3-way Jandy valve between the pump and cartridge filter, or a Tee fitting with a plug, to allow for vacuuming to waste.
Heavy Duty Floor Cleaning: Use Leaf Rakes to scoop the bottom of the floor, being gentle if there are large sticks and heavy debris in the pool. Keep at it until there is only very small dusty debris left in the pool, then vacuum the rest out of the pool. A garden hose vacuum, like the Leaf Gulper is also very helpful for pools that had a pool cover accident, or were left uncovered and neglected for many months, and are filled with large amounts of leaves.
Brushing the pool is very important after you get all of the debris out of the pool, and helps to get the small stuff off the walls and floor and into the filter.
Step Two: Balance the Water
There's no real reason to add any chemicals until you get all of the gunk out of the pool, so make sure that the pool is about 95% clean before you try to balance the water. Check your pH, Total Alkalinity and add any adjustment chemicals to get these right first. Your pH level should be on the low side, adjust it down in the range of 7.2 - 7.4. Total Alkalinity for vinyl pools should be at least 70 ppm. If your water is less Alkaline, add Alkalinity Increaser.
Calcium Hardness is the next thing to check and adjust. For vinyl pools, calcium should test at least 150 ppm. If you are under this, add calcium carbonate to increase the hardness of your pool water.
Cyanuric acid is important to check before you begin chlorinating the pool. Bright sun can burn off a lot of chlorine in a pool without at least 20ppm of cyanuric acid (conditioner or stabilizer) in the water. Add conditioner to the pool if a test shows the level is less than 20 ppm. If you do not have a test kit that can check all of these water balance levels - we have kits and strips with 1-day service (or you can take a water sample to a local pool store).
Step Three: Replace Some of the Water
If you pump a liner pool completely out, especially an inground liner pool, the liner may relax and wrinkles can occur when it's filled again. Using a vacuum to set the liner while refilling can be done, but if the liner is very old, it may shrink somewhat, and wrinkle or even tear when being refilled.
But ~ you can drain a third or half of the pool, and refill with a garden hose. Place a submersible pump on the top step in the shallow end, so that there's no danger of pumping out the shallow end. As long as you leave 6" of water across the shallow end floor, the liner should not relax, and give you no problems.
If you have a separate main drain line for your pool, use the main drain to drain the pool past the skimmers, just be sure to watch it, so you do not completely drain the pool! As the pool drains, hose and brush off the steps and walls if there are any dirt or stains, but do not use a pressure washer!
Step Four: Shock the Pool
After replacing 25-50% of green pool water with fresh water, and balancing the water chemistry again, your chlorine shock will be much more effective, so you won't need nearly as much. This saves lots of money, but also is gentler on a vinyl liner.
Check your pH level again, and lower if necessary. Then dissolve 1-2 bags of pool shock per 10,000 gallons, by pouring them into a 5-gal bucket that is filled with water. Use a stirring stick to dissolve and then pour the mixture around the pool edge. Add enough shock until the water turns a cloudy blue color, which shouldn't be more than 2 bags of shock per 10,000 gallons (some shocks are stronger than others).
Tried all That, Still Green
Are you filtering the pool 24/7? Go ahead and let the pump run, backwashing or cleaning the filter as needed. If you really tried all of my suggestions above, and you have a clean pool with balanced water (some of which is fresh refill water), and it's still not clearing after a few days... then I would recommend that you floc the pool. A flocculent is a chemical that bonds to anything floating in the water and sinks it to the pool floor. You have to be able to vacuum to waste all of the "jelly" that settles out the next day.
The only pool flocculent I would recommend for green cloudy pools is Phos Floc. Especially for pools that went very green, there is likely a high level of phosphates and nitrates in the water. PhosFloc not only clears the pool water, but it removes phosphates, which lead to algae growth.
Just follow the instructions, adjusting the pH to 7.0, and adding 4lbs of Phos-Floc per 10,000 gallons of pool water. At $5 bucks per pound, it's not our cheapest pool floc, but it's one that is almost sure to clean nearly any poor pool water condition (some pools may need secondary treatment).
SPP Pool Expert