How to use Bleach?

I have gathered from forum perusal that using bleach is recommended for algae. I have a semi-persistant green/yellow algae that won't leave me alone.

28,000 gal pool, salt-chlorine generator, in-ground

My FC level is wonderfully constant at 1.5 ppm (ideal range per my swc is 1.0 to 3.0) with the chlorinator on 75%, running 8 hours daily. I note that people are saying to use bleach, but in what quantity and how do you apply it? Do I go dump a gallon in the pool, dillute it first, etc?

I have used an algicide now at 2x recommended first dose to no avail.

To figure out what level of chlorine will kill your green/yellow algae, which may be mustard algae if it looks like powder, we need to know your CYA level. Also, if your SWG manufacturer recommended a high CYA level of 70-80 (which most do to ensure high efficiency of the SWG), then the minimum FC you should be maintaining is 3.0 ppm, not the 1-3 that they recommend. Even 3.0 is on the low side, but most people with an SWG seem to do OK with that, though a few battle mustard algae and need to set a higher setting of around 5-6 ppm.

So, first test your CYA level and also see if you can figure out of you have regular green algae, which will be free floating, or if you have mustard algae, which is yellow/brown and looks like dust. The amount of chlorine you will need to maintain until all the algae is killed is as follows, depending on the CYA level.

On this forum, the traditional chart to look at is at this post and you can certainly start by trying shock levels per that chart. If you find that the algae is not going away, then you can use the following chart instead which uses more recent information and understanding, but is less tested.

Code:

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CYA    Green    Mustard & Black
30      12.5      21.5
50      20.0      34.0
75      30.0      50.0

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As you can see, it takes quite a high Free Chlorine (FC) level to kill mustard (and also probably Black) algae, but the actual "active" chlorine concentrations are only 0.3 ppm for Green and 1.0 ppm for Mustard/Black algae. The high CYA levels cut down the effective "active" chlorine level. If you add some acid to get your initial pH lower (to around 7.2) then you may be able to use lower chlorine levels than shown in the above table since the large amounts of chlorine will raise the pH and lower chlorine's effectiveness.

Once you establish a high chlorine level, you then need to maintain it until all the algae is gone (which will require lots of filtering, so keep your pump running 24/7) and until the chlorine doesn't drop significantly overnight (initially it will drop as it kills and oxidizes the algae so you'll keep adding chlorine until that stops). The most important ingredient is patience. Then, when you are done, keep your FC level at least at 3.0 ppm, especially if your CYA level is high.

Good luck and keep us posted as to your progress.

Richard

Wow, thanks for the detailed reply Richard. At least now I understand the variables. If anyone will indulge my new questions:

1. How do you test CYA level? I have never used stabilizer, so I will reference my SWG manual when I get home and act accordingly. I don't, however, know how to test it after I add it. Which leads to my next question....

2. What method is best to test my FC and other stats? I have a little liquid-dropper test kit from a pool store, but I know the chart only goes to 3.0 ppm for FC and we're now talking of ranges up to 15. Plus, a few posts are referencing a test kit that I seem not familiar with.

3. As for pool shock, or maintaining a high FC level until the algae dies - are we talking about dumping chlorine bleach straight into the pool?

You can measure your CYA level with a CYA drops test, available in many test kits. CYA tests can also be ordered separately, if a kit does not provide for CYA testing.

While I and many on these forums have utilized and been very happy with "Ben's kit", aka the test kit from Pool Solutions, it appears to be unavailable at this time. This thread:
http://www.poolforum.com/pf2/showthread.php?t=6326
will list some alternatives, including some with good clearance prices. Although Wal-Mart carries an HTH 6-way kit that is often written about here as an alternative, I wouldn't recommend it for you as it has only 2 tests for CYA, does not measure free chlorine, and only measures total chlorine up to 5.0.

Finally, yes, you'll just be dumping straight bleach into the pool - in the deep end in front of a return with the pump running. You use the Bleach Calculator to determine how much to put in, depending on how much you want to increase your chlorine level.

Quote:

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Originally Posted by windfix

Wow, thanks for the detailed reply Richard. At least now I understand the variables. If anyone will indulge my new questions:

1. How do you test CYA level? I have never used stabilizer, so I will reference my SWG manual when I get home and act accordingly. I don't, however, know how to test it after I add it. Which leads to my next question....

2. What method is best to test my FC and other stats? I have a little liquid-dropper test kit from a pool store, but I know the chart only goes to 3.0 ppm for FC and we're now talking of ranges up to 15. Plus, a few posts are referencing a test kit that I seem not familiar with.

3. As for pool shock, or maintaining a high FC level until the algae dies - are we talking about dumping chlorine bleach straight into the pool?

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Windfix, I just added a little to your MD post, anyway, I'll still say - WELCOME TO THE FORUM! Richard (ChemGeek) always gives good advice, if you ever have a chemistry ? he's one of the 'go to guys' here. Before I start answering your questions, let me advise you to give www.poolsolutions.com a good read (if you haven't already) - it's the starting place for this forum and many of the ideas or 'techniques' that are advocated here.

#1 - Testing cya level is done with a drop based kit which includes a specific test for it, it is probably the dyi test that has the most subjectivity (you and I could do the same test with the same kit on the same water and come up with quite different results - however, we'd have a 'decent' idea of what the cya reading is). Most installers will add the cya when they start up the pool and it tends to stay around (it only leaves the pool via splashout or backwashing/ draining the pool), there are also a couple types of chlorine that add cya with the cl. You most probably have some in your water even if you've never added any, which is why it's important to know how much is in there as it effects the ability of the chlorine in the pool to do it's job.

#2 - The best method of testing is to accurately do your own testing with a good kit (the PS234 is considered to be the best by the folks who use this site [unfortunately, there are some 'irregularities' with shipping and availability right now, but you can order one from the link I gave above], the second favorite is the Taylor 2006, which is available in many places - both can measure up to 50 ppm chlorine (but you can also use the 'shot glass method' with your test kit - a search should find a number of hits)

#3 - YUP! Dump the bleach right into the pool, if you do it in front of an active return, you'll get better/ quicker distribution. It is fine to use with your SWCG as it's the same stuff that you're producing.

I hope that this will at least start to answer your questions, I'd imagine that you can cull some useful info from it and I'm sure that others will 'pop in' to offer more help.

Good luck with your pool, feel free to ask for more info if it's needed. :)