Anyone ever try a UV light for algae? No more green!

Algae problems in swimming pool water.
Green (cloudy) water or slimy pool walls.
Black algae. Mustard algae. Pink or white pool mold.
Traz
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Anyone ever try a UV light for algae? No more green!

Postby Traz » Sat 22 May, 2010 14:50

I am tired of dealing with green water. I have had a pool since I was a kid & never seem to have problems with green water. The past 2 years that is all I seem to deal with. Last year I gave up & covered the pool much earlier than usual so I didn't have to deal with it. So uncovering this year I still have the mess to contend with. I was going to drain it & start over but the local pool people said my liner will likely shrink & crack if I drain it.

Anyway, I was wondering if anyone has ever tried a UV light on their pool to kill the algae? We put one on our Koi pond last year & it worked miraculously to clear the algae. I have an extra powerful pond pump & thought about ordering another larger UV light to run the pool water through. Our pool is a 24 round 52" (or 54") deep above ground so I am estimating 14000 gal. The UV light I am looking at will handle 16000 gal.

I did see online something similar made for a pool but the pond one is probably the same idea. I wouldn't run it all the time, but thought I would try it before I start adding a bunch of chemicals.

If anyone has tried it or knows why it wouldn't work I would be interested to hear.


chem geek
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Anyone ever try a UV light for algae?

Postby chem geek » Sat 22 May, 2010 19:17

The problem with UV or ozone or any system that disinfects or kills only in the circulation system is that it does nothing for the bulk pool water until it circulates through the system (which in a pool takes hours) and does nothing for pathogens (including those in biofilms) or algae stuck to pool surfaces. For a pond where the volume isn't huge and the time for a turnover of water isn't very long, this can help control algae, but this doesn't work as well for a pool. There are plenty of saltwater chlorine generator (SWG) pools that can get algae if the FC is too low for the CYA level in spite of any algae getting killed when it goes through the SWG cell.

Chlorine alone can prevent algae growth but you need the Free Chlorine (FC) level to be high enough relative to the Cyanuric Acid (CYA) level. For manually dosed pools, the FC should be at least 7.5% of the CYA level. For saltwater chlorine generator (SWG) pools, the FC should be at least 4.5% of the CYA level. You can learn more by reading the Pool School which teaches you how tens of thousands of pool owners maintain their pools with chlorine alone (usually bleach or chlorinating liquid, unless they have an SWG) and no algaecides, no phosphate removers, no clarifiers, no flocculants, no enzymes, no UV, no ozone, no metal ions and no weekly shocking.

If you use only stabilized chlorine (e.g. Trichlor or Dichlor), then your CYA level will likely build up. The following are chemical facts independent of concentration of product or of pool size:

For every 10 ppm FC added by Trichlor, it also increases 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 at least 7 ppm.

So even with a low 1 ppm FC per day chlorine usage, continued use of Trichlor will increase CYA by over 100 ppm in 6 months if there is no water dilution.

I only use 12.5% chlorinating liquid in my 16,000 gallon pool shown here and here plus a small amount of acid every month or two. I have a fairly low chlorine usage of around 1 ppm FC per day due to an opaque electric safety cover, though the pool is used every day for 1-2 hours on weekdays and longer on weekends. It costs me only $15 per month in chemicals and I add chlorine twice a week. It doesn't get much simpler or less expensive than that. Without a pool cover, however, you would probably need to add chlorine every day or two.

Richard
Traz
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Anyone ever try a UV light for algae? New question added

Postby Traz » Sun 23 May, 2010 13:18

OK Thanks for the info. I have read some of the stuff on here & would like to try the bleach. The pool on opening was mostly clear but the bottom was covered with all kinds of green & debris. We did a sweep direct to waste until everything was so stirred up we couldn't see the bottom anymore. Now it is pea soup green.
I took a sample of water to the local pool place today to get initial readings before putting anything in it. Bought some test strips, filter socks & stopped at Aldi's for lots of bleach.
The readings were as follows.

Total Alkalinity 130 Range 130-150
Shock Treatment 0
pf 6.8 Range 7.2-7.6
cyanuric acid 0 Range 25-100
Total Hardness100 Range 200-450
Total Chlorine 0 Range 1-3
Free Chlorine 0 Range 1-3

We have a 24 foot round 52" deep (I think 52, or 54)
Jacuzzi cartridge filter.

So as I understand I can use the bleach. For shock levels am I looking to reach 10? No measurable stabilizer. How long do I need to keep it at 10? Until clear or just until green is gone? Should I correct any other levels before I use the bleach?
Thanks!

I did add some stabilizer to the filter basket using a sock using the pool calculator.
chem geek
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Anyone ever try a UV light for algae? New question added

Postby chem geek » Sun 23 May, 2010 18:23

Don't use too much stabilizer. You'll need less chlorine to get rid of the algae of the CYA level is lower. Read Defeating Algae . Also note that you can sometimes get chlorinating liquid at 10% or 12.5% strength at your local pool store or big-box store at a reasonable price. I use 12.5% chlorinating liquid I get from my local pool store at a reasonable price of $3.00 per gallon (before tax) and they reuse the bottles which is better than recycling.
Traz
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Anyone ever try a UV light for algae? New question added

Postby Traz » Sun 23 May, 2010 21:42

Our local place does carry the liquid cholrine but it was cheaper to get the 6% at Aldi's for $1.36 even though I had to use 2x's amount. Reusing jugs is nice, less waste.

Added the bleach & less stabilizer than called for. When I retested in an hour the total choline was higher than my test kit reads but the Free chlorine on the dip sticks still registered 0. I also added some PH increaser since I started at 6.8. After a few hours it was 7.2, the total chlorine still above my kits ability & nothing for free chlorine. The stabilizer I added to the sock in the skimmer did all disolve, it was granules. Went to dinner came back & pool is definitely a lighter green. Went from pea soup to a cloudy mint green. I can actually see the pole from the sweeper all the way to the bottom of the pool.
I rechecked (by now it is dark) Ph shot up high. I actually had some trouble telling exact number but probably 7.8! Free chlorine barely measurable & total chlorine dropped a little. Since I don't want to let up I added another 1 jug of bleach figuring no sun at night will keep it working well. I will test one more time tonight & then see what I have in the AM. I am not going to try & correct the ph any more tonight until I see what it is in the AM.
I have to find one of the test kits that measures higher numbers of total chlorine. I will take another sample to the pool place tomorrow to see what they have in readings.

Thanks again for all the suggestions.
chem geek
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Anyone ever try a UV light for algae? New question added

Postby chem geek » Mon 24 May, 2010 01:58

You can get a better test kit such as the Taylor K-2006 here or the TF-100 here with the latter kit having more volume of reagents so is close in price per test. If you just need the FAS-DPD chlorine test, you can get that here or here with the latter kit having more volume of reagents.
Traz
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Anyone ever try a UV light for algae? New question added

Postby Traz » Mon 24 May, 2010 16:06

I thought I was going to be able to get a kit locally from Leslies but it wasn't the right one so i will be ordering a kit.
This AM pool still cloudy green. About the same as last night. I took a sample to local pool place to see where things were.
Ph is high at 8.1
Total Alkalinity 150
Cyanuric acid 30
total hardness 260
Total chlorine 8.1
free chlorine 1
Shock treatment 7.1---what is this? I didn't add shock The paper says 0 normal range & recommended super shock which I told them I was not adding.

I ran the zodiac on the bottom today & it cleaned up a lot more dead broken down leaves & a brown slimy much stuck to the filter sock. Sides of the pool don't appear slimy at all. I did have a yellow ring around the top of the pool I am guessing is pollen.

Seems like the free chlorine isn't going up. It was very sunny today so I didn't add bleach as I figured it would be worthless. I will hit it again soon once the pool is in the shade. Our solar cover is shot or I would stick it on to try & preserve the levels.

Should I correct the pH 1st? I see many use muriitic acid to correct. Is that in the powder stuff for pH minus of pool chemicals or where do you buy it??? Not sure what I am looking for.
chem geek
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Anyone ever try a UV light for algae? New question added

Postby chem geek » Mon 24 May, 2010 20:34

The pH can read falsely high when the chlorine level is high, but since the FC is low the pH reading is probably roughly correct. So yes, I would add some acid to lower the pH. You can get Muriatic Acid at a hardware or big-box store. If you can get the half-strength 15-16% acid for half the price of the full-strength acid (31.45% hydrochloric acid) then that will fume less. Either way, pour downwind very slowly over a return flow in the deep end with the pump running and then lightly brush the side and bottom of the pool after you've added the acid. You want to ensure it is thoroughly mixed (the same is true with chlorine if you add that manually).

If the FC and TC readings are correct, then you do need to add more chlorine to oxidize the CC (TC-FC) and clear the pool. You hit it hard and consistently to keep the FC up at shock levels which for 30 ppm CYA is around 12 ppm FC. Lower the pH first, then wait at least 15 minutes (assuming you've got good circulation) and then add the chlorine.
Traz
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Anyone ever try a UV light for algae? No more green!

Postby Traz » Tue 25 May, 2010 21:26

Whoo hoo. No more green We have gone from swamp brown nasty green to pea soup green to mint green & now no green but very cloudy... all with bleach! Can't wait to see it tomorrow.

I lowered the ph back some tonight by adding the muritic acid. And gave it another blast of bleach.
I still don't have my test kit but the strips keep saying no FC. I don't believe it since there has been such a drastic improvement in the past few days. I took a sample to the pool store but it was too early & they weren't open..

Anyone know if Lighthouse will take back unopened chemicals? I just got them at their big beginning season sale. Since I don't plan on using all their stuff. They may not be happy about it , but I need a new solar cover so if I offer to buy that maybe they won't mind as much. If not I am pretty good at raising a rukus. :evil:

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