Stable High Free Chlorine But Still Green Water

by PCDiem
(Learn everything about clearing up a green pool in this eBook)

I have a 15,000 gal pool with a chlorine feeder that I keep filled with tri-chlor tablets. My pool test has been in good balance for weeks (pH 7 - 7.4, free chlorine 3 - 5 ppm, TA 80 - 100, CYA around 30).

We have prairie grasses around the swimming pool which started shedding their seeds which wind up in the pool in massive amounts. I suspect they're the source of my problem. How to clear up cloudy pool water and how to clean green pool step by step.

A few days ago, the swimming pool was green in the morning. I brushed the sides, vacuumed and shocked with 3 lbs. calcium-hypo. The free chlorine level has been over 10 ppm (water testing strips only go up to 10) for days yet the water still has a green tint. I don't want to drain and refill pool.

This morning I was cleaning the swimming pool and there was visible green on the floor, which I vacuumed to WASTE. I'd like to get a test kit to measure total and free chlorine more accurately but have no way to measure total or combined chlorine right now (other than a test kit that only goes up to 3 ppm).

My question this: Is it just a matter of giving it more time to kill the algae? I assume that since the water is still green tinted, there is still live algae.

I also assume that since the free chlorine level is staying high that adding more shock will not do anything besides prolong the wait for the chlorine level to drop to a swim-safe level. Am I right in these assumptions or should I be continuing to add more shock to the swimming pool?

Thanks for the question and picture

First I'd encourage you to get a Taylor FAS-DPD K-2006 test kit. A good test kit makes all the difference in the world.

Pool water test app
Pool Water Testing

Water Testing Kit

You can't trust test strips to calculate CYA on a consistent basis. You'll also do alot of guessing. Have you taken your pool water in to be analyzed? A
very low or very high CYA might be the problem.

The CYA must be in proportion to the chlorine, and vice versa. CYA should be 7.5% of the free chlorine level. If you run the chlorine at 2.5ppm, you'll run the CYA at 33.

2.5 divided by 7.5% = 33

Let's say hypothetically that the CYA is off, or low. This means the strips aren't giving you a true and accurate reading.

To get rid of the algae you'll need to shock the pool with Dichlor. This will not only put chlorine in the pool, it will also put in CYA.

Be careful when using Dichlor as it can get out of hand quickly. For every 10ppm of chlorine added with Dichlor, you'll raise the CYA by 9ppm. For every 10ppm of chlorine added with Trichlor tabs you'll raise the CYA by 6ppm.

Here are some good posts to look over:

Why Can't I Clear My Green/Blue Pool Water?

Green Pool Water

Swimming Pool Algae

I would highly recommend getting your water tested by a pool store very quickly and make the right adjustments if needed.

After you get the CYA in line, you can switch to liquid chlorine. I'm recommending this because cal. hypo. might increase the hard water levels.

Keep manually dosing the pool in the evening, keeping the chlorine level at 12ppm, or over. Retest in the morning.

If the chlorine level has dropped by half or more, either you do have an algae problem or the CYA is off, either too high or too low. Keeping filtering 24/7 and back wash once per day. Keep the water level up 1/3 - 1/2 up from the bottom of the skimmer.

Let me know about the water testing so we can get your pool up and running.

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To post a reply, or if you have a similar question, you can see your post on the Q&A page in the "Algae/Green Pool Water" category.

Swimming Pool Questions and Answers

Check back to this post for answers.

Hope this helps and have a fun and safe swimming season.


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