Pool Keeps Getting a Little Algae

[magnetar68]

Problem:

I have an in-ground plaster pool. It has been getting a slight film of brown-green algae on the walls and corners. I am having a difficult time getting to the crystal clear water I have had in the past.

Background:

I bought the house about 5 years ago, but this year I am having trouble maintaining the pool. Up until now, I have just been taking the water to the pool store every couple weeks. They gave me a print out, sold me some stuff, and I followed the dosing instructions. The irony is that I took a fair amount of chemistry in high school and college and have a fairly sophisticated coral reef aquarium, so I believe I have the technical background for maintaining a pool myself but until now I have not really brushed up on it. It was just one more thing to have to learn, and what I was doing seemed to be working, so I kept doing it. I added solar panels this year, so the temps are higher than previous years. This also means we use the pool more. I go to two different pool stores. Leslie's is closer, but the service there can be horrible. I also go to Aquarius in Walnut Creek, and they seem very knowledgeable, but are not open on Sundays and are farther away.

Here's some of the drama. After seeing some algae film last weekend, I went to Leslie's with a water sample. The guy at Leslie's told me my Chlorine was too high (yes high). My pH was also a little high, so he said I had plenty of Chlorine but at pH of 8.0, it would not work. I had added 2 lbs of granular Chlor Brite about 5 days before, so I guessed that could have been true. He also said I was probably not running my pump long enough. Bringing the pH down and running the pump almost 24 hours per day did clear up the pool a fair amount, but by this weekend, the pool had some algae again. I went to Aquarius on Sat, and they gave me the readings below, but my Chlorine was basically gone. They told me to bring down the pH (2 quarts of Muratic Acid) and then two hours later add 3 gallons of liquid chlorine. I only added 2 gallons, but this definitely helped a lot and the pool is better today, although not perfect. The pH was higher again today (8.2), after coming down yesterday, so I added 2 more quarts of acid today. pH still seems high, but I have no idea how reliable my test hit is.

Anyway, after all of this I spent some time on this site today. Assuming it is accurate, this site seems to have more knowledge than the stores. I order the TF-100 test kit so I can do the testing and dosing myself. I think I see my main issue. With my CYA over 150, I need a much higher level of chlorine. I find it somewhat surprising that neither of the two stores mentioned this Chlorine/CYA relationship, but if pool store information is anything like local fish store information, I should not be surprised. Using the www.poolcalculator.com, it says I need to change out 75% of the water volume to reduce the CYA concentration. This will cost me $800+ dollars.

So, finally, my questions:

1. Do I really need to reduce my CYA? (I assume the TF-100 test will help me get an accurate value here)
2. I don't see any Mobile RO units in the San Fran Bay Area online, does anyone know of one?
3. If I need to drain the pool,
   1. Is it safe to drain 75% of the water, or can emptying the pool cause it to crack?
   2. Is there a DIY on how to do this that is safe for an in-ground plaster pool?

Specs:

Type: In-ground, plaster
Dimensions: roughly rectangular, 30'x14' with a 3' shallow end and 8' deep end
Volume: I use 18,000 gallons for my calculations
Temp: 82-90F (depends on outside temp and sun)
Filtration: 2100 rpm from 7am to 7pm (24 hours lately)

Equipment:
Intelliflow VS 3050 pump
Pentair Clean and Clear Cartridge (200),
Suntouch Controller

Sanitizer:
Chlor Brite Sodium-Dichloro-s-Triazinetrione-Dihydrate (99%)Ganular
4x 3" Jumbo Tabs Trichloro-s-triazinetrione (99%)
Just switched to Liquid Chlorine yesterday.

Sun: Fully in the sun from 11am to 5pm in mid summer

Chemistry (From Lamotte WaterLink Spin Lab):

Saturday:

Free Chlorine: 0.55 ppm
Total Chlorine: 0.55 ppm
Combined Chlorine: 0 ppm
pH 8.2
Hardness: 250 ppm
Alkalinity (w/stabilizer correction): 97.7 ppm
CYA: 151+ ppm
Copper: 0 ppm
Iron: 0.1 ppm
Borate: 7 ppm

 

[MBG75]

Your staring off right by getting the TF-100!
If the cya is really that high, you'll have to replace water.
The experts should post here soon to help out.

By the way, another fellow Reef keeper here!

 

[scott.MI]

II will start out by saying you should start using pool math instead of pool calculator. Has a tab/link at top of the page. Also, when you get your test kit, make sure you do the extended test method for testing CYA over 100. See #9 in this post http://www.troublefreepool.com/thre...Kit-Directions?p=203524&viewfull=1#post203524

Do you NEED to lower your CYA, well you don't NEED to, it can be done, and has been done before managing a pool with high CYA. Of course, managing a pool with high CYA is different than SLAMing a pool with high CYA. Now, any amount that you do lower it will make it that much easier and have you needing to maintain a lower chlorine level and using much less chlorine to SLAM as well as using less test reagents. Keep in mind pool stores are not very accurate at testing any levels of CYA let alone very high levels so using the 75% drain number right now is a little hasty although it could end up being worse, just no way to tell until you test it.

I'll let others comment on how much you will safely be able to drain at one time. It may be helpful to know your location for this.

I don't know that anyone has actually done RO as it is rare and supposedly very costly.


I will leave you with a glimmer of hope. ASSUMING the CYA reading of 151 was close to accurate, a 75% drain would get you down to 40 according to poolmath. You could certainly get by without having to lower your CYA down that far if the cost of water is too much of a concern. Some people raise their CYA to 50 or 60 for comparison. The other way to look at it is by switching to bleach and away from dichlor and trichlor, it won't have to be done again.

 

[magnetar68]

Thanks for the responses. I added my location my profile.

 

[magnetar68]

High CYA, What would you do?

My pool was having algae trouble. I added a lot of liquid chlorine and now the pool looks great, but my chlorine levels are very high. I am new to this stuff, so I need some guidance on what to do. I received by TF-100 test kit today and took some tests. I also took a sample to the store. The two tests don't agree, but I don't know if their tests or the TF-100 tests get affected by high chlorine. They use a Motte WaterLink Spin Lab.

Here the data I have:

TF-100 Tests:

FAS-DPD Test
FC 34 drops * 0.5 = 17 (+/- 10% = 15.3 to 18.7)
CC = 1 drops * 0.5 = 0.5 CC
TA 11 drops * 10 = 110
CH 12 drops * 25 = 300 (+/- 10% = 270 to 330)
CYA (90+ version of test) 60 ml *2 = 120 (+/- 30 = 90 to 150)

Motte WaterLink Spin Lab:

FC 18.42+
TC 18.42+
CC 0
pH 8 (high due to FC level?)
CH 115 (low due to high FC level?)
TA (w.stabilizer correction) 69
CYA 150

Assuming the TF-100 test are correct, I think I have at least couple of options.

(1) Work with the high CYA until the end of the season and drain and fill the pool later
(2) Drain and refill the pool now to correct the CYA level

If (1) what should I let the Chlorine levels come down to 5? 8? 10? ? I realize the chart here says that the Target FC level for a CYA of 100 is 12, but several people have said you cannot swim in a pool with a FC of 12. I honestly don't know who to believe. I guess I could be a guinea pig and give it a try to see if I can get any irritation. The guy at the swim store who maintains a lot of pools in the area says he keeps his high CYA pools at a FC of 5.

If (2) how long will it take to re-balance the pool? Is this a (a) couple of day process, (b) week long process, or (c) a two week process?

 

[tim5055]

Re: High CYA, What would you do?

Trust your TF-100 numbers. I took over my pool when I purchased my house last November and had CYA 200+. Pool stores I went to said the CYA was fine, don't bother with it. But they always seemed to be lining me up to sell me something.

I found this site and began reading Pool School. The information seemed well laid out and it all seemed to make sense. With my CYA level I had to search out one of the older CYA charts that went that high and found my minimum FC was 8 and my target was 15. I started adding bleach and got it up to 15 and kept it there. When the water got above 70 we began swimming. The wife even questioned me because "she thought I kept the chlorine high" and she didn't "feel that". Through aggressive back-washing and several partial water exchanges I'm now down to 80 CYA so I keep my FC between 6 - 9. I feel no difference in the pool between the way it was and now.

Only you can decide whether you are going to follow the methods taught at TFP or "The guy at the swim store who maintains a lot of pools". I will caution you, don't try to mix pool store advice and TFPC advice. It won't work!

You haven't indicated anything that would require a SLAM (unless I missed something) so other than the CYA, I really don't see anything you can't get in order in an afternoon.

To quote the owner of this site

Throughout TFP, you will read that we suggest certain levels that good science and practical experience has taught us fall within safe ranges.

Further reading of posts here will draw you to the inescapable conclusion that these guidelines work.......in thousands and thousands of pools worldwide.

You may or may not choose to use these methods and guidelines or you may use some and not others. Our goal is to teach you what has been proven time and time again and then let you use that information to your benefit.

 

[Abigail K]

Re: High CYA, What would you do?

Short answer because you have been on this forum since 2010, post back if you don't understand.

We don't trust pool store testing, especially the CYA levels. Members have gotten 3 different results from 3 different stores.

FC recommendations of 1-3ppm are from the days before CYA was discovered. CYA buffers how harsh the FC actually is. With CYA 120, your minimum FC is 9.

Ignore adjusted TA.

If you had algae trouble, then you would need to SLAM, in which case we would recommend a partial drain and refill.
SLAM takes as long as it needs, it is a marathon and not a sprint.

 

[scott.MI]

Re-balancing a pool should be very quick and simple, like part of a day. PH is simple to balance, TA is simple to raise and doesn't really need to be lowered since it will get lowered any time you need to lower PH. If you want a better idea, you can post test results of your fill water PH, Ta, and CH. With pool math and your test kit, there is nothing to balancing a pool.

If your concerned about the FC levels suggested for maintaining your pool with 120CYA...then you just need to drain so you can enjoy your pool, keep it clean and sanitized without worrying about those big FC numbers. What good is a pool if you can't enjoy it cause your worried about too much chlorine, or if your trying to use less chlorine and an algae problem starts. If your not prepared to keep the FC above the minimum for your CYA of 120, you may not have enough active chlorine to do what it needs to do.

Deciding to drain now or later is all up to you. I'll end by saying that my understanding is swimming in a pool with 120CYA and FC of 15 should be no harsher than swimming in a pool with 60 CYA and FC of 7.