Green Pool Treatment

[StarBrightPools]

Hello Everyone! I just joined today and have some concerns about a green pool. Yesterday Oct, 10 2009 I checked out a customers green pool. I am still very new at this, so please bare with me.

The chlorine level was 0, ph 8.0, TA:90;Calcium 170; and cya 60ppm. This was using the Taylor Complete DPD Test Kit K-2005.

First I cleaned the filters, and then I brushed the walls and steps. I then proceed to add 8gallons of chlorine(Probably too much), 1g of Muriatic acid(Definitely Too Much), and 8ozs of dropout(recommends 4oz per 10,000g). The pool is approximately 20,000g.

I then let the 3/4hp pump circulate the water for 18hours. I went back today and tested the water. There is no FC and the ph is 7.0. The water is not as green but still present. So does that mean that the algae consumed the 8gallons of chlorine with a 10% chlorine percentage? Based on the size of the pool, should I add 3 more gallons to help kill the rest of the algae, and have it circulate for only 7hours based on Pentairs Energy website? And if and when I add more chlorine and cycle the pump again, will the dropout that is in the pool do its job after another cycle?

Thank you for any insight on this.

[chem geek]

8 gallons of 10% chlorinating liquid in 20,000 gallons would raise the Free Chlorine (FC) by 40 ppm. The 1 gallon of Muriatic Acid, if full-strength (31.45% Hydrochloric Acid) would lower the pH from 8.0 to 6.9 (with TA 90 and CYA 60). The chlorinating liquid would raise the pH back to around 8.0 though as the chlorine gets used up the pH will drop back towards 6.9.

Your test kit uses a DPD chlorine test and this will bleach out above around 10 ppm so you won't be able to easily tell if there is chlorine in the water. If you have an inexpensive OTO test (shades of yellow) it won't bleach out and will become orange or even brown at very high chlorine levels. The best chlorine test to use is the FAS-DPD chlorine test since it will not bleach out (more powder can be added if you see a flash of pink) and it can measure up to 50 ppm and can measure chlorine accurately to within 0.2 ppm with a 25 ml sample, 0.5 ppm with a 10 ml sample, or 1 ppm with a 5 ml sample. You can get a FAS-DPD chlorine test based on Taylor reagents here since you already have the other Taylor tests, or you can get the TF100 kit here that also includes an OTO chlorine test in addition to the FAS-DPD (as well as other tests similar to the Taylor K-2006 -- a comparison of the test kits is given here. In the meantime, you can dilute the pool water by 4:1 with filtered or distilled water (water that doesn't have chlorine or monochloramine in it) and use your DPD kit to see if you see any pink/red.

As for whether a pool can consume that much chlorine, it is possible if the chlorine gets to zero and bacteria convert CYA into ammonia. You are still measuring substantial CYA so that is less likely unless the level used to be higher. If you measure the chlorine level correctly and there is none, then get an inexpensive ammonia test kit from a fish/pet/aquarium store. If you measure ammonia (which can also be monochloramine since the test does not distinguish) then it takes at least 8 times the ammonia amount as chlorine (FC) so yes this can be substantial.

By the way, shocking a pool with chlorine to kill algae is NOT a one-time event. You add chlorine and measure it within hour and then shock again to MAINTAIN a high chlorine level. For a fast algae kill, the FC should be maintained at around 40% of the CYA level or around 24 ppm in your case, assuming your 60 ppm CYA reading is accurate. If you have ammonia in the pool, the chlorine will get consumed by it very quickly in an hour or two in most cases (at higher CYA levels it can take longer, but still be fairly fast given the amount of chlorine you added).

Richard

[StarBrightPools]

8 gallons of 10% chlorinating liquid in 20,000 gallons would raise the Free Chlorine (FC) by 40 ppm. The 1 gallon of Muriatic Acid, if full-strength (31.45% Hydrochloric Acid) would lower the pH from 8.0 to 6.9 (with TA 90 and CYA 60). The chlorinating liquid would raise the pH back to around 8.0 though as the chlorine gets used up the pH will drop back towards 6.9.

Your test kit uses a DPD chlorine test and this will bleach out above around 10 ppm so you won't be able to easily tell if there is chlorine in the water. If you have an inexpensive OTO test (shades of yellow) it won't bleach out and will become orange or even brown at very high chlorine levels. The best chlorine test to use is the FAS-DPD chlorine test since it will not bleach out (more powder can be added if you see a flash of pink) and it can measure up to 50 ppm and can measure chlorine accurately to within 0.2 ppm with a 25 ml sample, 0.5 ppm with a 10 ml sample, or 1 ppm with a 5 ml sample. You can get a FAS-DPD chlorine test based on Taylor reagents here since you already have the other Taylor tests, or you can get the TF100 kit here that also includes an OTO chlorine test in addition to the FAS-DPD (as well as other tests similar to the Taylor K-2006 -- a comparison of the test kits is given here. In the meantime, you can dilute the pool water by 4:1 with filtered or distilled water (water that doesn't have chlorine or monochloramine in it) and use your DPD kit to see if you see any pink/red.

As for whether a pool can consume that much chlorine, it is possible if the chlorine gets to zero and bacteria convert CYA into ammonia. You are still measuring substantial CYA so that is less likely unless the level used to be higher. If you measure the chlorine level correctly and there is none, then get an inexpensive ammonia test kit from a fish/pet/aquarium store. If you measure ammonia (which can also be monochloramine since the test does not distinguish) then it takes at least 8 times the ammonia amount as chlorine (FC) so yes this can be substantial.

By the way, shocking a pool with chlorine to kill algae is NOT a one-time event. You add chlorine and measure it within hour and then shock again to MAINTAIN a high chlorine level. For a fast algae kill, the FC should be maintained at around 40% of the CYA level or around 24 ppm in your case, assuming your 60 ppm CYA reading is accurate. If you have ammonia in the pool, the chlorine will get consumed by it very quickly in an hour or two in most cases (at higher CYA levels it can take longer, but still be fairly fast given the amount of chlorine you added).

Richard

Thank you for the links for the better test kits. I was told that you could dilute the pool water to obtain a more accurate reading of the CYA present. Like a 1:1 ratio of distilled water and pool water. Is that correct?

Also I was going to use 2lbs of Calcium Hypo-chlorite because it offers a higher level of available chlorine. But if the pool does indeed have over 10ppm of chlorine, should I not proceed? With anything above that amount, shouldn't it have destroyed any traces of green algae? Also if the test for ammonia does show it is present; how do I proceed? If none is present, what is the next step? You said it takes at least 8 times the ammonia amount as chlorine. Did you mean it takes 8 times the chlorine amount?

I also realize that the Cal Hypo will increase total hardness. Would you happen to know by how much?

I also did not know that bacteria could convert CYA (Cyanuric Acid) into ammonia. I was told the only way to dispose of CYA is to drain the pool partially and add fresh water. I also realize that there could be a high CYA readomg even if you were to drain the whole pool and refill with fresh water. Which would not be recommend due to the possibility of the pool to become dislodged from the ground.

I will be purchasing the OTO test kit and an ammonia tester tomorrow.

Thank you very much.

[chem geek]

Usually you only dilute the water for the CYA test if the reading is very high such as above 100 ppm. For 60 ppm, you should be able to read it accurately. Dilution adds additional error to the test so it's not that much better doing dilution 1:1 and multiplying by 2 for the test though you can certainly do that if you wanted to.

You would only use Cal-Hypo for shocking if you intentionally wanted to increase the Calcium Hardness (CH) level. For every 10 ppm FC added by Cal-Hypo, it also increases CH by at least 7 ppm. There is absolutely nothing wrong with using chlorinating liquid (or bleach, for that matter). Yes, it takes more by weight to get to the same FC level, but all that matters in the water is the FC level you achieve and maintain. So I'm not sure why you want to use Cal-Hypo at this point.

Yes, I meant that it takes a chlorine FC that is 8 times the measured ammonia ppm. It's unlikely for the bacteria to have converted CYA to ammonia in this pool since usually if the pool has gone bad for a while, the CYA goes nearly to zero if such conversion occurs. Though bacteria can convert CYA into ammonia, it's not a reliable way to reduce CYA and you are left with ammonia that takes a lot of chlorine to oxidize. Every 1 ppm of CYA that is degraded requires around 3 ppm FC to get rid of. Technical details are in this post.

To lower CYA levels, one usually does multiple partial drain/refill.

You can read Defeating Algae for more info. Normally, a large amount of chlorine would turn the algae in the pool from green to gray as shown here so something unusual may be happening in this particular pool you are working with. It's possible that there was copper in the pool so that at a higher pH it turned the water greenish and that this may be remaining causing the cloudy algae to still look greenish. As the chlorine level drops, the pH should drop so that could help clear up any copper-based green tint (hopefully you won't have copper stains on pool surfaces as a result). If any copper-based algicide was used, then that could be a source of copper in the pool.

[PaulR]

If you've measured CYA at 60 there's no reason to run a test with diluted water; 60 is in the range the test is designed to measure.

Also if you just measured CYA 60 on the 10th, there's no reason to suspect it has all been converted to ammonia since then. If the green is clearing up, the most likely reason for an FC drop is that it has been killing the algae, as it is supposed to do.

--paulr

[StarBrightPools]

Update. I went back to the pool October 16,2009 and added 4gallons of chlorine and 1 1/2 orange cups of Alum Sulfate. I also made sure I increased the TA and ph levels so that foaming would not result. I then went to go turn on the pump, and nothing. Find out the starter coil on the motor was bad due to condensation. So I replaced the motor the next day and vacuumed out the pool. Performed a top sweep and pool looks a cloudy blue. Much better now. I did not add a clarifier unfortunately.

The water level was low, so I told the homeowner to fill to the proper level and super chlorinate and run the pump for 3 days. I also added 2 cups of Soda Ash because the ph was still 7.0. I will check the results out tomorrow.

Also when I tested the chlorine it had 3 FC last Saturday. And I cleaned the filters again. They were green.

Thank you all again.