Green Algae coming back week after week...

Algae problems in swimming pool water.
Green (cloudy) water or slimy pool walls.
Black algae. Mustard algae. Pink or white pool mold.
CalHypoK
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Green Algae coming back week after week...

Postby CalHypoK » Mon 06 Jul, 2009 15:29

Problem: Hey everyone, I'm new to the board! I'm facing an issue with my pool and can't seem to figure out what the problem is. I feel like the chemistry in right on but my equipment may be the issue. My filter reads 5 psi in filter mode, then 10 psi in backwash mode. Could it just be low on sand?

I vacuum the pool to waste each week because new green algae forms regularly. I've been using more and more Cal Hypo to keep algae from blooming but it isn't doing the trick. Last week it bloomed with 3ppm chlorine in the pool. The water temp is up at about 90 degrees F right now.

Let me know what questions you have to further draw a conclusion, thank you very much in advance.

FC: 3ppm
TC: 3ppm
pH: 7.3-7.4
TA: 100
CH: 200
CYA: 60

My pool: 20 x 40, 8ft deep end.
Pool chemicals: Using 65% Cal-Hypo weekly, with 3" tabs in my automatic Hayward chlorinator.
My pump & filter: 1.5HP Hayward Superpump, S-220T Hayward High Rate Sand Filter, 1.5" plumbing

Other info: I'm also using a poly 60% for algae prevention.

.


chem geek
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Green Algae coming back week after week...

Postby chem geek » Mon 06 Jul, 2009 18:07

Where are these measurement numbers coming from? If from a pool store or from test strips, I wouldn't trust them. Even if they were accurate, at 60 ppm CYA you would need to maintain a minimum FC of at least 4.5 ppm to prevent algae from growing -- 3 ppm FC is too close to the edge. You basically need to keep the FC at a minimum of 7.5% of the CYA level in a manually dosed pool (SWG pools can usually get away with an FC that is 4.5% of the CYA level). However, I suspect your CYA level is actually higher than 60 ppm if you've been regularly using Trichlor tabs/pucks.

You should shock with chlorinating liquid or bleach so that you don't keep increasing your CH level. The following are basic rules of fact independent of concentration of chemical or pool size:

For every 10 ppm Free Chlorine (FC) added by Trichlor, it also increases Cyanuric Acid (CYA) by 6 ppm.
For every 10 ppm FC added by Dichlor, it also increases CYA by 9 ppm.
For every 10 ppm FC added by Cal-Hypo, it also increases Calcium Hardness (CH) by 7 ppm.

Even at a low chlorine usage of 1 ppm FC per day, continued use of Trichlor as a sole source of chlorine would increase CYA by over 100 ppm in 6 months if there were no dilution of water. Read the Pool School for more information on maintaining your pool and in particular read Defeating Algae to shock your pool with a high enough chlorine level to kill all the algae (at 60 ppm CYA that's around 24 ppm FC). You'll need a good test kit, either the Taylor K-2006 you can get at a good online price here or the TF100 from tftestkits.net here with the latter kit having 36% more volume of reagents so is less expensive per test.
tastywaves007

Green Algae coming back week after week...

Postby tastywaves007 » Tue 07 Jul, 2009 22:46

Have you tested your Phosphates level in your pool? If you are above 200 this could be a contributing factor. Throw in the recommended dosage of phosfree to your pool and it should take care of it. Ask your local Pool store supplier.
chem geek
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Green Algae coming back week after week...

Postby chem geek » Wed 08 Jul, 2009 01:35

A phosphate remover is like an algaecide (it removes a nutrient algae needs to grow). It's one way to control algae, but not the only way. I have 2000-3000 ppb phosphates in my pool (my fill water has 300-500 ppb phosphates added by the water district for corrosion control and I have blown in fertilized soil) yet I keep my pool free of algae growth by maintaining an appropriate Free Chlorine (FC) level relative to Cyanuric Acid (CYA). One can certainly use a phosphate remover or an algaecide, both at extra cost, but it is not necessary and one can use chlorine alone to keep away algae.
tastywaves007

Green Algae coming back week after week...

Postby tastywaves007 » Tue 28 Jul, 2009 21:23

I know MAINTAINING a good chlorine level will keep it away. however in this case it has already set in. I recommended that just getting rid of what the algae is using to grow (phosphates) would remedy this person's immediate problem in a couple of weeks along with maintaining the appropriate chlorine level.
chem geek
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Green Algae coming back week after week...

Postby chem geek » Tue 28 Jul, 2009 22:14

It there is already an algae bloom or cloudy water or more than a 1 ppm Free Chlorine (FC) drop overnight, then the pool needs to be shocked with chlorine (using chlorinating liquid or 6% unscented bleach) at a higher level (FC that is 40% of the CYA level, so 24 ppm in this case) to kill off the algae and oxidize the organics. If one is just in maintenance mode, then one needs to keep the FC (in a manually dosed pool) at a minimum of 7.5% of the Cyanuric Acid (CYA) level.

If one is unable or unwilling to maintain an FC appropriate to the CYA level, which in this person's case with a CYA of 60 ppm is an FC of at least 4.5 ppm, then they can use either a PolyQuat 60 algaecide weekly without fail or can use a phosphate remover as you described. It is not necessary, but if they can't consistently maintain the appropriate FC/CYA ratio, then it's certainly an option for them. Another alternative is to have 50 ppm Borates in the pool, though this only helps and won't completely prevent algae if the FC drop towards zero.
Mgara

Green Algae coming back week after week...

Postby Mgara » Sat 01 Aug, 2009 13:07

I don't know what is with this stuff, but everyone I know using it including myself loves it. Go to nomor.htm and use the drop down to find the product for your problem. I had problems with yellow algae and it was gone in 2 days, including the stains in 4 more days. It keeps my water so clear and the chemical balance is somehow maintained with this product. It's summer and I have even been able to turn down the time my pool pump runs and still no problems.
chem geek
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Green Algae coming back week after week...

Postby chem geek » Sat 01 Aug, 2009 16:29

No Mor Problems is sodium bromide so essentially turns your pool into a bromine pool. Bromine doesn't combine with Cyanuric Acid (CYA) so works around a high CYA level, but bromine breaks down in sunlight (though not as quickly as chlorine if no CYA is present) so your chlorine usage will be higher (chlorine reactivates bromide to bromine).

This is just a workaround for a high CYA level. You could instead just maintain an appropriate FC/CYA ratio using chlorine alone. You are probably using Trichlor pucks/tabs and these increase the CYA level. Read the Pool School for more info.
Marklora

Green Algae coming back week after week...

Postby Marklora » Sun 23 Aug, 2009 12:28

I have the same problem with algae growing on walls and floor the last two seasons. My CYA level is 80 and I use Trichlor 3 inch tabs. What do suggest I do? I keep my free chlorine level at 5. To got higher on the free chlorine level would the level be safe? Should I go to Bromine or there another tab I should use? Thanks
chem geek
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Green Algae coming back week after week...

Postby chem geek » Sun 23 Aug, 2009 16:54

If your CYA is truly 80 ppm (and if this is from a pool store, I wouldn't trust the number -- get a Taylor K-2006 test kit of a TF100 test kit from tftestkits.net), then the minimum FC in a manually dosed pool is 6 ppm to prevent green algae growth. I suspect your CYA level is actually somewhat higher or that the minimum FC sometimes drops below 5 ppm. At any rate, if you don't want to keep increasing the CYA level you need to use chlorinating liquid or 6% unscented bleach, but that needs to be added every day or two unless you have a pool cover in which case you can often add it twice a week. That's the tradeoff between Trichlor and liquid forms of chlorine -- convenience vs. cost.

You CAN use Trichlor in spite of higher CYA levels if you supplement with algicides or phosphate removers to help prevent algae growth (both at extra cost) and also shock weekly with chlorinating liquid or bleach to help oxidize bather waste and organics that build up due to the chlorine being less effective at the higher CYA levels. See the Pool School for more info.

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