Q&A: My pool is green. Can you help?


I have an on ground pool that we have been struggling to control algae growth. (16×32, sand filter, salt generator)
I have my water tested at our local pool company  with the following results:
temp 78
colour green
we have a salt chlorinator -it hadn’t been working but was replaced on saturday so I’m not yet sure if it is working. I’ve added 4 bags of salt and the level is reading 6.3 or 2850
pH 8.4
CYA 35
TA 180
Ca 59
borate 45
Phosphate 300


How old is your filter, and filter media? Are you using sand? If it has been more than 3-5 years since you changed the sand, that should help.

How big is the pool? Liquid Chlorine is the fastest acting way to treat algae in my experience. If you are shocking to a level reading 10ppm, the pH results should not be trusted as the high chlorine will mask/alter your results. Wait until the chlorine comes down to get an accurate pH reading. High pH can also cause a green tint to the water. Salt generating systems often run higher pH because the chlorine that is generated has a very high pH. of about 8.5. To control the impact of the high pH in a salt pool an alkalinity of 180 should be reduced until it is in the lower acceptable range of 80-100. As the pH increases the chlorine efficiency goes down.

We recommend that a pool is backwashed when the pressure increases by 5-7ppm. How often this happens depends on the age of your filter media, if you have used the system to vacuum, and your environment around your pool like a lot of trees and debris. I often backwash during and after vacuuming my pool, as well as when I notice the jets are not as powerful as they usually are. If the filter needs to be backwashed, that can cause the filter to be inefficient, and it can take longer to remedy an algae issue.