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Winter in AZ, Algae, and should I drain my pool? - Swimming Pool Help

Winter in AZ, Algae, and should I drain my pool?

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Winter in AZ, Algae, and should I drain my pool?

Postby Phlimm » Sat 22 Nov, 2008 14:35

I live in Phoenix, AZ and have an in ground chlorine cleaned Pebble-Tec pool with a sand filter. I am using a Taylor K-2005 Test Kit.

Last season we struggled with constant algae growth and had to blast the hell out of the pool several times with bleach and such. It would work for several weeks, then go bad again. Up and down, up and down.

So now it is November and too cold to swim. We never have to add antifreeze or anything like that because it never gets that cold and we run the pump every night, with the little vacuum bug as well. BUT right now it is a green swamp, and I want this to end before next spring.

We do all our own maintenance - I own the home and want to really understand how to take care of the pool and not just throw money to a pool guy.

Another pool owner told me that I need to drain the pool every few years and totally replace the water. This seemed reasonable to me especially after all the dang chemicals we added last season. I was using 3" pucks in a float with Cl and Cyanuric Acid in them and it got to like 80 ppm CyAcid which is when we hit the Chlorine lock and started getting algae issues. I did several backflush / refill cycles which again helped in the short run, but nothing seemed to be a permanent fix. We switched to nothing but bleach for a bit, but that got to be a real pain in the patootie adding more and more every few days.

Also a Leslie's guy told me that draining from the bottom is better than a backflush for getting rid of Cyanuric Acid because it settles.

SO...are you with me still? :)

Should I:

Drain and refill completely
Drain and refill partially from a backflush
Drain and refill partially from the bottom
NOT Drain and use more chem treatments

Also...I KNOW that people use the tabs in a float and have gorgeous pools. HOW do I keep the Cl / Cyanuric acid levels nicely balanced using the tabs? Once I get to an optimum CyAcid level, are there tabs with just Cl in them?

And...sorry that this is a novel...I am a n00b here...whenever I test for Cl, the total and free levels always seem the same. Why is that? What should it look like? According to my test kit that means that my combined chlorine is zero?!?! Huh???

1000 thanks and blessings on you to anyone who is able to help out with any or all of the above! :D
Phlimm
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Winter in AZ, Algae, and should I drain my pool?

Postby aquamom » Mon 24 Nov, 2008 12:47

Hi!

Sorry you have to deal with a green pool that is totally no fun!! First can you post a full set of test results for your pool? Is your pool vinyl lined? Approx how many gallons does it hold?

What do you use to mainly sanitize the pool? Pucks are notrious for screwing up your water chemistry and I don't advise using them, unless you are going to be on vacation and don't have someone to add some CL to the pool while you are gone.

First thing is to post these results and then someone can help more further.

CL
FreeCL
TotalCL
pH
TA
CYA
Calcium(though not to important if vinyl lined, but still good to know)
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Winter in AZ, Algae, and should I drain my pool?

Postby Phlimm » Tue 25 Nov, 2008 09:46

Well as I said in the original post, it is a Pebble-Tec pool and I was using 3" tabs for most of the time, but went to bleach for a bit it try to fix the chlorine lock. The pool is about 13,500 gallons.
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Winter in AZ, Algae, and should I drain my pool?

Postby chem geek » Tue 25 Nov, 2008 13:45

There is no such thing as chlorine lock. What happens is that continued use of stabilized chlorine products, such as Trichlor tabs/pucks or Dichlor granular/powder, increases the Cyanuric Acid (CYA) level and that makes chlorine less effective unless you proportionately increase the Free Chlorine (FC) level to compensate. Algae starts to develop and this initially is seen as a hidden chlorine demand as chlorine gets used up faster than the tablet dissolves. Eventually, the water turns cloudy and then green (for green algae). At 80 ppm CYA, if your FC level got below 4 ppm then the chances get high for getting green algae if the pool has nutrients (phosphates and nitrates). For manually dosed pools, 6 ppm FC is the minimum target at 80 ppm CYA.

If you want to use only Trichlor as your source of chlorine, then you have to use a supplemental algaecide to prevent algae growth -- either weekly PolyQuat 60 or use of a phosphate remover (both are extra cost -- around $2-3 per week for your sized pool). Either that or you have to dilute your water enough to keep the CYA level lower. With Trichlor, for every 10 ppm FC that it adds, it also increases CYA by 6 ppm. With Dichlor, for every 10 ppm FC that it adds, it also increases CYA by 9 ppm. Unstabilized chlorine does not have CYA, but Cal-Hypo has calcium. With Cal-Hypo, for evey 10 ppm FC that it adds, it also increases Calcium Hardness (CH) by 7 ppm. The other alternative is to use chlorinating liquid and bleach (6% Clorox Regular unscented) which do not have calcium nor CYA, but you would need to add it every day or two unless you have an opaque-to-UV solar cover and even then would need to add chlorine about twice a week. There are automatic dosing systems for such liquid chlorine sources.

Unfortunately, there is no solid slow-dissolving source of chlorine that does not contain CYA. Lithium hypochlorite is a powder fairly concentrated in chlorine, but it is very expensive and it dissolves quickly. Dichlor contains CYA and dissolves quickly. Cal-Hypo, as mentioned above, does not have CYA though does have calcium and though it is usually granular it does come in pucks requiring a special feeder (NEVER put them into a Trichlor feeder), but they tend to break down too quickly and leave a messy residue.

It's not true that draining from the bottom removes more CYA because in most pools the circulation is good enough that the CYA is well dispersed. If you don't believe that, then invert a sample tube and put it down near the bottom, turn it over, then raise it out of the water and test such "bottom" water compared to water about a foot down from the surface -- you should find all the measurements are similar except possibly the FC level might be a little higher in the depths on a sunny day.

You are right that when Total Chlorine = Free Chlorine that this means that Combined Chlorine (CC) is zero and that's a good thing and a normal situation. CC is chlorine combined with other compounds, usually ammonia. When you measure any CC, it means that not enough chlorine is available to get rid of the ammonia (and urea) from your sweat (and urine). It's rare to see in a residential pool unless the bather load is high and the FC gets too low or the CYA level is very high (as these slows down the rate of elimination of CC). By the way, even though chlorine combines with CYA (which is why CYA makes chlorine much less effective) these "chlorinated cyanurates" measure as FC because chlorine is released from CYA relatively quickly (in seconds). However, it's the "active" or instantaneous chlorine (hypochlorous acid) concentration that determines the rate at which chlorine kills bacteria, inactivates viruses, kills or prevents algae growth, oxidizes swimsuits and hair, etc. and that active chlorine concentration is roughly proportional to the FC/CYA ratio.

Take charge of your pool and learn more at the Pool School at Trouble Free Pool (including the article on defeating algae). The first step is getting a good test kit. The Taylor K-2005 isn't bad, but the Taylor K-2006 is better or the TF100 from tftestkits(dot)com. You can just get the FAS-DPD chlorine test here since that will give you the equivalent of the K-2006 given what you already have -- this FAS-DPD chlorine test measures Free Chlorine (FC) and Combined Chlorine (CC) with 0.2 ppm resolution (using a 25 ml sample; 0.5 ppm resolution using a 10 ml sample) and the test does not bleach out at high FC levels so can measure up to 50 ppm (useful when shocking a pool).

Richard
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Winter in AZ, Algae, and should I drain my pool?

Postby Phlimm » Tue 25 Nov, 2008 19:54

Richard -

Thanks so much for the info on chlorine! I was confused for sure about TC, FC and CC. I am surprised that there is no non-CYA tabs available. Living in Phoenix, I DEFINITELY do not want to use Cal-Hypo!

So here is my remaining question - would it be better to totally drain the pool and refill it with fresh water so I can start from zero as far as chems go? Or should I just tackle the chem balancing with the water I have (minus any partial drain to level out the CYA)?

I was told you need to do a full drain/refill every few years regardless from one person, but another said that draining a pool of all the water is an invitation to disaster. Being that it is not a vinyl pool, it could not pop out, but is there something else that could happen?

Thanks a lot!
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Winter in AZ, Algae, and should I drain my pool?

Postby chem geek » Tue 25 Nov, 2008 21:53

Actually, a plaster/gunite in-ground pool can indeed pop out if the water table is high. So you are right to be concerned about a full refill. Fortunately, even if you had to do a complete water replacement, you can do so with the "sheet" method where a very large sheet that is larger than the pool then covers it and you remove water from under the sheet and add water on top of it. The sheet drops and when it gets to the bottom, you remove the sheet and have a nearly complete water replacement. Use of multiple large silage bags is another similar approach.

It doesn't sound like you actually need to do that much of a water replacement. Just do a partial drain/refill to lower the CYA level, attack the algae outbreak with chlorinating liquid, and go from there.

As for how often water needs to be replaced, the rule you heard is partly due to overuse of stabilized chlorine and a buildup of CYA. If you are careful with that, then the only significant buildup is salt and that takes longer than just a couple of years. If you have a filter you backwash weekly, then you are doing partial dilution already, but if you have a cartridge filter, then you'll have to do more manual dilution unless you have enough winter rains to overflow/dilute (in Phoenix, I'll bet you don't get that much rain).

With ANY source of chlorine, for every 10 ppm FC this gets converted to 8 ppm salt. With hypochlorite sources of chlorine, specifically chlorinating liquid, bleach, lithium hypochlorite, for every 10 ppm FC it immediately adds 8 ppm salt so the total salt from these sources is 16 ppm. If your chlorine usage is 2 ppm FC per day, then over an entire year that's around 600 ppm salt so you can see that it would take several years before that builds up (if there were no dilution).

Richard
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