Why Your Pool Keeps Turning Green Even When the Chlorine Looks Fine
Your chlorine reads normal. You brushed the walls last week. And the pool is turning green anyway.
When homeowners in La Vernia and San Antonio call us about a pool that will not stay clear, the culprit is very often something a basic test strip never shows: phosphates. Phosphates are food for algae. You can dump chlorine in all summer, but as long as the food supply is there, the algae keeps coming back to dinner.
High phosphates are one of the most common problems we find in water around here, and most pool owners have never even heard of them.
1. What Phosphates Are and Where They Come From
Phosphates are nutrients. Great for your lawn, terrible for your pool. They wash and blow into the water from everyday sources:
- Fertilizer and lawn runoff after rain or sprinklers
- Leaves, grass clippings, and other yard debris breaking down in the water
- Fill water itself, especially well water
- Sweat, sunscreen, and body oils from swimmers
- Some pool chemicals, including certain metal and stain treatments
You cannot see phosphates, smell them, or feel them. The only way to know your level is to test for it.
2. Why High Phosphates Cost You Money
Algae eats phosphates. Chlorine kills algae. So when phosphates run high, your chlorine spends its whole life fighting a battle it cannot win, and you pay for it three ways:
More chemicals. A pool with high phosphates burns through chlorine faster because it is constantly working against new algae growth. You are essentially paying to sanitize the same water over and over.
More algae blooms. Levels above 500 ppb (parts per billion) start giving algae a real advantage. Above 1,000 ppb, you have a buffet, and one hot week or one missed chlorine dose can flip a clear pool green in days.
Cloudy, dull water. Even before a full bloom, high phosphates can leave water looking tired no matter how much you brush and shock.
If you have ever wondered why your neighbor uses half the chlorine you do, phosphates may be the answer.
3. The Fix Is Simpler Than You Think
The good news: phosphates are one of the most treatable problems in pool care.
- Test the water. A proper phosphate test tells you exactly where you stand. Ideally you want levels down near 100 ppb or below.
- Treat with a phosphate remover. These products bind the phosphates so they can be filtered out of the water. Follow the dose for your pool size, run the filter, then clean the filter afterward, because that is where the phosphates end up.
- Cut off the source. Keep fertilizer spray away from the pool deck, skim debris before it sinks and breaks down, and rinse off heavy sunscreen before long swim sessions.
- Retest. Phosphates creep back in over time, especially after storms. A quick check every month or two during swim season keeps you ahead of it.
Get Your Water Tested Free at Bear Foot Pool Supply
Here is the easiest first step. Our sister store, Bear Foot Pool Supply in La Vernia, tests your pool water for FREE. No appointment needed. Just bring in a water sample, and in a few minutes you will know your phosphate level along with your full water chemistry. If the phosphates are high, the treatment you need is right there on the shelf, along with straight answers about how to use it.
A lot of folks walk into Bear Foot for chlorine tabs and walk out finally understanding why their pool would not stay clear all summer. One free test can save you an entire season of frustration.
Final Thoughts: Stop Feeding the Algae
Chlorine alone is not a plan. If your pool keeps sliding green, or your chemical bill keeps climbing, test for phosphates before you spend another dollar on shock.
And if you would rather hand the whole thing off, that is what we do:
- ✔ Free water testing at Bear Foot Pool Supply in La Vernia
- ✔ Phosphate treatment done right the first time
- ✔ Weekly cleaning service that keeps levels in check
- ✔ Licensed, insured, and local to La Vernia and San Antonio
Pool Fix has 20 years of experience keeping pools in this area clean and healthy, and we know exactly what the local water throws at them. Call us at (210) 465-2386, or stop by Bear Foot Pool Supply and let the water test do the talking.