How to Kill Giardia in Pools

Remove all flotation devices from the pool water and keep everyone out of the water. Fill the pool with water if needed so the water level is at the center marks on the skimmer faceplate. Backwash the pool and filter for two to three minutes.

Use the pool test kit to test the pH level of the pool water. Adjust the water using pH reducer or increaser to achieve a pH as near to 7.0 as you can get, but no more than 7.2 and no less than 7.0. This is critical before adding aluminum sulfate, which turns into gel-form when added to the water.

Follow the directions on the aluminum sulfate package. Generally, the range of product to use is between 4 to 8 pounds of aluminum sulfate for every 10,000 gallons of water in the pool. Broadcast the product into the pool water and not into the skimmer. The aluminum sulfate will capture suspended particles and dirt floating in the water when it turns to a gel-like form and settle on the bottom of the pool until you vacuum it up. Run the pool filter for four hours, or until the pressure gauge is in the red so the product circulates in the water. Turn off the filter when the gauge reaches this level and let the water sit for six to 12 hours.

Turn the valve handle to waste if you have a multi-port handle. If you have a slide handle, lift up on the handle so it is in the “backwash” position. Vacuum the pool using the vacuum head, hose and skimmer plate. Move the vacuum slowly across the pool floor to vacuum up the alum, but move the vacuum slowly so you do not stir up the alum on the bottom or the alum and the suspended particles it has captured in the water will start floating again.

Test the alkalinity and pH of the water and adjust as needed so the readings are within the desired range of 7.2 to 7.8.

Add shock to the pool during the evening, just after the sun sets. For extreme conditions such as giardia contamination, use 2 pounds of shock per every 10,000 gallons of water in the pool. Turn on the pool filter for a full cycle, which is eight hours.

Steam-clean all of the floatation devices and any other swimming pool equipment to remove any giardia cysts. This includes parts of the ladders and steps that are not in the water and driving broads and any boundary ropes. Anything that has been in the pool must be cleaned.

Backwash the pool filter after the shock has circulated for at least eight hours.

Repeat steps 2, 3 and 4 to flocculate the pool with aluminum sulfate one more time.

Test the water after you have flocculated the pool for the second time. Adjust the chlorine level, pH and alkalinity levels so each is in the ideal range, which is 7.2 to 7.8 for pH and 2.0 to 3.0 for the chlorine. Use sodium thiosulphate to lower the chlorine level if it is high.

Take a water sample to your local health department or pool dealer to have it tested. Assuming the water tests negative for giardia, you can open the pool for swimming.