dark green pool - how do I clean it??

Algae problems in swimming pool water.
Green (cloudy) water or slimy pool walls.
Black algae. Mustard algae. Pink or white pool mold.
chem geek
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dark green pool - how do I clean it??

Postby chem geek » Wed 20 May, 2009 04:27

For a manually dosed pool, you want to target a minimum Free Chlorine (FC) level that is 7.5% of the Cyanuric Acid (CYA) level and never let it get below 5% of the CYA level. Read the Pool School for more info on how to maintain your pool.


bobbyg714
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Dark green pool - how do I clean it??

Postby bobbyg714 » Thu 28 May, 2009 07:03

Richard,

Just wanted to give and update and ask a couple of follow-up questions.
Update: The pool looks great. Water is sparkling clear and with the new D.E filter it looks better than it ever did. Thank you again for all of your advice. I also love the test kit and being able to test the water daily, what a help to know where I am at all times.

My current levels are as follows:

FC- 9.5
PH - 7.6
TA - 110
CYA 100

Now that I finally understand the FC/CYA relationship I have maintained at least a 7.5% FC level. I also believe that my two mid-season algae issues the past two years have been because I didn't realize how high the FC should be with my CYA where it is. I have also switched from using the pucks for chlorination to liquid bleach. That brings me to my question.

Am I ok at with keeping these levels where they are as long as I remain diligent with the 7.5% rule, or should I consider draining some water and bringing my CYA level down. The funny thing is when I personally test my CYA I repeatedly get 100. I have had two different pool stores test and they get 45 and 40. I believe my Taylor kit and not their levels. I mean one store employee told me that using Powder Power Plus does not impact my CYA level at all. Is this true? I know I have used Powder power the past three years heavily because of the algae issues. Have you seen wide ranging CYA reading before?


So do you recommend me trying to bring that level down at all? Is there any harm at maintaining a FC level of close to 10?

Thanks in advance,

Bob
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dark green pool - how do I clean it??

Postby chem geek » Thu 28 May, 2009 12:48

Bob,

As to whether you maintain a minimum FC of 7.5 ppm (absolutely never let it get below 5 ppm) with your 100 ppm CYA or whether you dilute the water to lower the CYA level is up to you. At the high CYA level your chlorine daily drop from breakdown from sunlight is probably very low. Do you know what it is? Can you compare the overnight drop in FC to the daytime drop? Even at 80 ppm CYA you should get a substantial reduction in chlorine drop from sunlight. That's the main issue with lowering it to 50 ppm or below -- you may end up using more chlorine per day (even at the lower proportional FC level).

The main downside to having the CYA so high is that IF you ever let the FC level drop too low and algae starts to grow, then killing the algae takes a lot more chlorine since the shock level for a quick algae kill is an FC that is around 40% of the CYA level -- clearly 40 ppm FC is a heck of a lot of chlorine. The algae will still get killed at a lower level, say 20% of the CYA level, but it takes far longer once a bloom is started.

Other choices you have for "insurance" to prevent (or slow down) algae growth even if the FC drops too low are a weekly PolyQuat 60 algaecide or use of a phosphate remover. These are at extra cost. You could also add 50 ppm Borates to the pool as a mostly one-time cost where this is a mild algaecide (algistat) and a pH buffer and adds a shimmer or clarity to the pool by lowering the surface tension of the water. This is optional, but I recently added it to my pool and I like it. This article talks about adding borates to a pool. This post in that thread gives some sources for Boric Acid if you didn't want to go the 20 Mule Team Borax and Muriatic Acid route.

You can absolutely manage your pool using chlorine alone and I've done that for years (at around $15 per month for a 16,000 gallon pool with an opaque pool cover and around 1 ppm FC per day chlorine usage), but if you want "insurance", then you have options. My pool has 2000-3000 ppb phosphates so is rather unforgiving if the FC/CYA ratio get too low (below 5%) so we'll see if this changes with the Borates (I'll do an experiment at the end of the pool season letting the FC get to zero and seeing how long it takes for the water to turn dull/cloudy with algae growth).

As for Power Powder Plus, this is Cal-Hypo (calcium hypochlorite) so it does not increase CYA, but it does increase Calcium Hardness (CH). For every 10 ppm FC added by Cal-Hypo, it also increases CH by at least 7 ppm. You did not post your CH reading -- what is it?

As for the CYA reading the pool store is getting, they often do this test incorrectly (and other tests as well). However, to ensure that you are doing it right, see this link with photos from Taylor and also see if you can look down the tube in front of you at around waist/stomach level with the sun behind you outside. You want strong indirect light, not direct sunlight nor weak indoor lighting (strong indirect indoor lighting is OK).

An FC of 10 ppm with a CYA of 100 ppm is technically equivalent (i.e. has the same hypochlorous acid concentration) as a pool with 0.1 ppm FC and no CYA. Your pool is far less reactive than most indoor pools. My wife experiences this difference every winter season when her swimsuits have to get replaced (elasticity gets shot) after just one season of use when using a community center indoor pool with 1-2 ppm FC and no CYA while in our own outdoor pool with 3-4 ppm FC and 30 ppm CYA the suits last for years (many summer seasons). Also, her skin is flakier and hair frizzier when using the pool with no CYA. The difference is that our outdoor pool is equivalent to around 0.1 ppm FC with no CYA so the indoor pool has 10-20 times the rate of oxidation and is essentially "over-chlorinated". It also likely is producing disinfection by-products such a nitrogen trichloride at a higher rate as well, but that's another topic.

Richard
bobbyg714
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Dark green pool - how do I clean it??

Postby bobbyg714 » Thu 28 May, 2009 14:33

Richard,
Just retested CYA outside in better light waist level. Came in at 90. A little better. Sorry left out CH. CH is 250. I have a vinyl liner. Does rain water dilute CYA at all or is it only draining the water that helps. I am ok at keeping the level where it is as adding the bleach is easy. I test in the am and adjust. As far as FC drop off, what should I do? Test at night and then test again first thing in the morning?

Bob
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dark green pool - how do I clean it??

Postby chem geek » Thu 28 May, 2009 15:12

If the rain overflows the pool, then it will dilute everything in it including the CYA. If the rain just raises the pool level without overflowing and the water level then drops over time with evaporation, then there will be no change in the amount of CYA (or anything else) in the pool.

For the overnight test, yes, test after the sun goes down and test in the morning as early as you reasonably can before the sun hits the pool for too long.
mcoolong

Dark green pool - Can someone explain "standard 6% bleach"

Postby mcoolong » Sun 31 May, 2009 07:41

Just found your forums. Some good info. We have an above ground pool with a vinyl pool liner. It is approx 5000 gallons. Was reading where someone talked about using "standard 6% bleach." Is this your regular groceries store Chlorox style bleach? Or a special made bleach for pools. I have a grocery store generic bleach. But it doesnt list the chemical breakdown for it. ie: what percentage of actual bleach. (I am assuming this is what you are talkikng about.) We got most of the floating particles out of it. We put some baking soda in. We did do some shock first but i don't think enough. We took a sample to a local pool place and they gave us a report.

saturation ldx -3
TDS 200
CYA 0
Tot.Chlorine 0
Free Chlorine 0
pH 6.2
Tot. Alkalinity 10
Adj Total Alk 10
Tot. Hardness 46
chem geek
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dark green pool - how do I clean it??

Postby chem geek » Sun 31 May, 2009 17:40

If their report is correct, then you need a lot of adjustments. The TA can be raised with baking soda and that will raise the pH somewhat as well, though a little pH Up (Arm & Hammer Super Washing Soda) can also be used in addition to the baking soda. You should probably add at least a little Calcium Hardness (up to 100-150 ppm) to prevent foaming. You also need some Cyanuric Acid (CYA) -- you could use Dichlor as your initial source of chlorine to add both chlorine and CYA at the same time since for every 10 ppm Free Chlorine (FC) added by Dichlor, it also increases CYA by 10 ppm. Just be careful not to use too much and should probably shoot for no more than 30 ppm CYA until the pool gets clear.

You can use chlorinating liquid, which you can get from the pool store or a hardware store, or 6% unscented bleach, which is either Clorox Regular or an off-brand Ultra bleach. An off-brand regular bleach is probably too weak at around 3% and has too much excess lye in it.
Howlleo

Dark green pool - how do I clean it??

Postby Howlleo » Thu 04 Jun, 2009 18:30

Hi,

I've been reading around and basically, the idea I'm getting is that you keep the pool in continuous shock while vacuuming and backwashing until the algae is gone. And you keep the pH in line while you do this.

Question: exactly how often should I be shocking the pool? The first day, the rest of the week... I'm trying to estimate how much bleach to buy, and the number is ginormous if I'm getting the right idea here.

I have a 26,000 gallon (I think) in-ground, vinyl-lined backyard pool, so I guess I need about 6 gallons of 6% bleach per shock. If I shock five times the first day and twice a day after that for a week... that's 102 gallons. :shock: I'll need a truck to get it to the car.

I'm missing something, right?
chem geek
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dark green pool - how do I clean it??

Postby chem geek » Thu 04 Jun, 2009 21:38

The answer completely depends on how much algae there is in your pool and how much you are relying on the chlorine to clear it vs. physical removal via scooping, skimmer socks, and filter cleaning/backwashing. If done properly, and not half-heartedly, it takes less chlorine since you kill the algae quickly at first. See this post where it took 7 gallons of chlorine to clear.
Howlleo

Dark green pool - how do I clean it??

Postby Howlleo » Sat 06 Jun, 2009 21:09

I think this pool might be bigger... Also, the filter (Nautilus NS32) seems to need maintenance and I don't know how to use it. So - I know this sounds awful, but can you clean the pool with just vacuuming and bleach and a poorly running filter if necessary?

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