Green pool

[almeida]

We bought a 15' round Intex pool on Craigslist to get us through the early days of COVID. Well, COVID and the pool both lasted longer than expected, and here we are. We used chlorine tablets (the small ones) and DryTec calcium hypochlorite shock the first year and had no trouble at all. We drained it over the winter. Last year, we did the same and only had trouble once after being away for a few weeks. The pool was slightly cloudy when we got back (someone had been adding chemicals but not vacuuming), but it cleared up after a little shock and running the filter constantly. Again, we drained it over the winter. This year, we've been using chlorine tablets (the big ones). The pool had been so clear it almost looked like it was empty. I hadn't shocked it all. Then, we went away for just a few weeks, and all heck broke loose.

There was a partially-dissolved tab in the floating chlorine dispenser when we left, but it was totally gone by the time we got back. I only have AquaChek test strips, and they were showing total and free chlorine at basically zero. The water was cloudy. I put a new tab in and started running the filter 24 hours a day. That was on July 14th. The next day, the levels were still very low, maybe 1 ppm for total and free chlorine. I put in another chlorine puck and kept the filter going. The next day, the numbers were maybe 5 and 3 ppm for total and free. The water wasn't clearing up at all, so then I put in half a pound of the DryTec shock. The numbers were off the charts after that. They didn't really come back down until two days ago when they were reading in the 5/3 to 10/5 ppm range for total/free. By then, the water was getting cloudier and now was kind of green. The surface of the water had small pockets of foam. Just a small one inch patch here and there, but still something that stood out.

I was beginning to think my strips were off. I know they're not super accurate, but I thought maybe they were just wrong, so I took a sample to a pool store and had them test it:

Free Chlorine: 2.5 ppm
Combined Chlorine: 2 ppm
pH: 7.7
Alkalinity: 115 ppm
Hardness: <50 ppm
Cyanuric Acid: 100 ppm
Copper: <0.3 ppm
Iron: <0.15 ppm
Phosphates: 0 ppb
Borate: 0 ppm
LSI: -0.42

They said the hardness is too low, but that it didn't matter for vinyl pools. They said the cyanuric acid is too high. I had put in stabilizer myself, because I thought that's what you're supposed to do, but they said you don't really need it for these pools. They didn't say what to do about it, but the printout they gave me said the only solution is to dilute with fresh water. They recommended just shocking the pool and then maybe an algaecide. I put in another half pound of shock last night. This morning, the pool was definitely green and very cloudy. I could no longer see the bottom. The pictures are from this morning.

Here's what I have on hand:

AquaChek strips
Chlorine tabs
DryTec shock
Pool Mate Algae Destroyer (never used it myself)
Various alkalinity controls, stabilizers, pH risers and fallers, and an algae destroyer

We're in a heat wave, just like everyone else these days. I assume it's not safe to swim in green water. I assume my test strips aren't accurate enough to know whether it's safe to swim after shocking. I assume I won't be able to get more accurate test strips within the next few days. I assume there's a limit to what my little Intex cartridge filter can do to clean up the water. I figure my options are:

1. Mess around with chemicals for a few days or a week or more and have to keep everyone out of the pool
2. Drain it and refill it and let people swim, albeit in freezing cold water

I'm currently doing option 2. Am I wrong? Should I drain it completely or halfway or what? (Well, halfway isn't an option anymore because the pump is going faster than I expected. But draining two thirds is still an option!) I'm worried that I've got something funky growing and that it'll just come back if I do a partial drain. Then again, even if I did drain it completely, I've got nothing to really fully sanitize the empty liner, ladder, etc., so maybe it's silly to worry about getting rid of the funk entirely before refilling. Also, we're in a drought and really aren't supposed to be filling pools. I feel guilty about doing this already. The last picture shows how much is left in the pool and what it looks like. I just brushed the dark spots on the bottom, which I couldn't even see when I first went out this morning.

 

[zea3]

Hi, welcome to TFP! You made the right choice for your pool. When CYA is 100 ppm or more your only choice is a drain and refill. You want your CYA level to be between 30 and 50 ppm. If you drain 3/4 of the pool and then start refilling you should be good. You are also correct about your small intex filter. It will have a difficult time filtering all the dead algae out of the pool.

If you want to test your water with greater accuracy you need an FAS/DPD based kit. They cost more than strips but they will give you the accuracy you need to treat the pool correctly and prevent this problem from happening again. HTH makes an inexpensive 6 way kit that will get you through the rest of the swim season. https://www.amazon.com/HTH-1273-Swi...d=1658584644&sprefix=HTH+6+way,aps,164&sr=8-3

 

[almeida]

I drained it down to about 12" and and am now refilling. I'll go up to 42" or so, so not quite 3/4, but pretty close. Should I do anything in terms of prevention as it's filling up or just wait and see? I brushed the bottom and sides. There really wasn't much gunk anywhere. No slime or anything, except just a hint at the water line on the ladder. As I said, I have chlorine tabs and shock.

 

[zea3]

As for why your pool turned green in the first place, it is because the FC to CYA ratio was out of balance. The higher CYA goes, the higher FC must go to remain effective. CYA buffers and protects chlorine from premature burn off in the sun, but when CYA levels get too high it "protects" the chlorine so much it renders it ineffective. In your case with a CYA of 100+, you would have needed 11-13 ppm of chlorine to prevent the algae from taking over and 39 ppm of chlorine to kill the algae and clear the pool. Starting over with fresh water in a small pool with a small filter is your best option.

We teach the Trouble Free Pool Care method. The cornerstone of this method is accurate testing and understanding what each pool chemical does and how they interact with each other. This is not traditional pool care as you know it but it is based in proven science and it works.

Lets look at the test results from the pool store that you posted My comments in red:
Free Chlorine: 2.5 ppm By itself this is a little low by TFP standards. If your CYA was 20 ppm this would have been an acceptable FC level.
Combined Chlorine: 2 ppm Combined chlorine is the waste product of chlorine oxidation and is constantly created and broken down as your FC does its job. However CC over 0.5 ppm indicates a problem
pH: 7.7 This level is good anywhere between 7.0 and 7.8
Alkalinity: 115 ppm This level is good between 70 and 120 ppm. We usually only worry about it when adjusting pH. Keeping it in balance with pH helps keep pH stable.
Hardness: <50 ppm This is your calcium level (CH). In a vinyl liner pool it only needs to be between 50 and 450 ppm. If CH gets too high it can cause problems and requires draining to lower the levels.
Cyanuric Acid: 100 ppm This is your CYA. As I explained above it can cause problems if it gets too high. The only way to lower CYA levels is to drain and replace water. The pool industry refers to high CYA levels as chlorine lock.
Copper: <0.3 ppm You do not want copper in your pool, so it is good you are draining water. Copper can kill algae but it also causes stains on pool surfaces along with turning light colored hair and clothing green. Copper does not occur naturally in pool water so the only way it gets in is by adding products that contain copper to your pool. Check the ingredients of your pool products and avoid anything containing copper. The most common place to find copper in pool products is in algacide and some multi-purpose pool tablets. You don't need to add copper to chlorine to kill algae in a properly chlorinated pool.
Iron: <0.15 ppm Iron is commonly found in well water that was used to fill a pool. If you have a well you may need to keep an eye on iron levels, but it doesn't sound like you have an iron problem with your water.
Phosphates: 0 ppb Phosphates occur naturally in pool water. Pool stores like to get rid of all phosphates because they are algae food, however if you don't have algae you don't need to worry about phosphate levels.
Borate: 0 ppm Borates are added to water to improve the feel, regulate pH, and act as a mild algacide. They are not required to balance your water and many people do not use them.
LSI: -0.42 The Langlier Saturation Index. Not a chemical value but a scale to indicate if your water is balanced correctly. As long as your water is at the recommended levels your LSI will be fine. It is an advanced skill to look at LSI numbers that most pool owners don't need to worry about.

Traditional pool industry standards do not look at how these chemical values interact with each other. They look at each value as a stand alone as if the other values don't exist. In a perfect pool world, 3-5 ppm of chlorine will keep your pool clear if you have the minimum CYA of 30 ppm and it never changes. Most pool chlorine is sold in dry form and needs to be stabilized with CYA or calcium. If you use only pool tablets, a typical 8 ounce tablet will add 5.5 ppm of CYA and 3.3 of FC in a 10,000 gallon pool. By the way all levels recommended by traditional pool industry standards are based on a 10,000 gallon pool. Your pool is less than half that size at approximately 4000 gallons. In your pool that same 8 ounce tablet is adding 14 ppm of CYA and 8.3 ppm of FC! If you started the season with fresh water and did not add CYA separately, each dissolved 8 ounce tablet added 14 ppm of CYA to your pool. After dissolving 5 tablets you have added 56 ppm of CYA. At this point additional tablets will continue adding CYA, but the amount of chlorine added by each tablet will be too low and allow algae to grow. Also keep in mind it is adding chlorine over the course of the time it takes the tablet to dissolve, so you are not getting a dose of 8.3 ppm of FC all at once but slowly released over time, so algae is starting much sooner, but kills enough of it that your water may only look a little dull at this point. Bags of chlorine shock with dichlor or trichlor as the active ingredient also contain CYA. A 1 lb bag of shock will add 6.7 ppm of CYA and 10 ppm of chlorine to a 10,000 gallon pool. In your pool that translates to 17 ppm of CYA and 27 ppm of chlorine per bag. You can see how CYA numbers can get out of hand very quickly.

It looks like the shock you used contains calcium and not CYA. You can use that, just keep an eye on the calcium levels. a 1 lb bag of 65% calcium hypochlorite shock adds 14 ppm of calcium and 19 ppm of chlorine to a 4000 gallon pool. It would take a good while to get in trouble with calcium unless you start off with very hard water. Test the calcium level of your tap water and it will tell you how much cal-hypo you can use and stay within recommended levels.

To start your pool water, I would recommend adding 1 pound of CYA to the water, and use liquid chlorine to raise the FC level. With a CYA of 30 ppm your daily target for FC is 4-6 ppm and a minimum of 2 ppm. If you target 6 ppm then the FC should last a couple of days before needing to add more liquid chlorine. If you want to continue using tablets you will need to keep track of how much CYA you are adding so you can adjust the FC level as needed. I would still start off with adding 30 ppm of CYA, since it will take time for tablets to dissolve and you need some to start to prevent the chlorine from being too harsh on skin and hair and from burning off too quickly. When the CYA gets to 60 switch to liquid chlorine or use the cal-hypo shock and monitor the FC levels.

TFP has a free app called Poolmath that will help you determine how much of each chemical you need. You can find more information about it here: PoolMath

 

[almeida]

Thanks for all the information.

I have Pool Mate Jumbo Tabs: https://www.poolmateproducts.com/_files/ugd/e6e619_25f2536db9d945da9783af6fea88361f.pdf. The label says trichloro-s-triazinetrione. Is there a way to know how much CYA is in these tablets? Is the CYA in the trichloro-s-triazinetrione itself or is it hidden in the "other ingredients"? I have a 15 lb. bucket of these tabs and there were 30 tabs, so that's 0.5 lb. each. I used the app and put in 4627 gallons (15' by 42") and say I'm adding one 0.5 lb. of "Trichlor," it says it'll:

Raise FC by 12.0
Raise CYA by 7.2
Lower pH by 0.6
Raise SALT by 9.7

For the shock, mine says the active ingredient is calcium hypochlorite at 68% plus 32% of "other ingredients," and that the "minimum available chlorine" is 65%. Do I plug that into the app as "65% Cal-Hypo"? If so, then 1 lb. will:

Raise FC by 17.0
Raise CH by 12.0
Raise SALT by 17.0

My stabilizer just says the active ingredient is cyanuric acid but doesn't say how much. If I put it the app as "Dry Stabilizer," a 1 lb. shot will:

Raise CYA by 26.0
Lower pH by 0.5

This is pretty neat. The only thing I don't see is an option for alkaline control. Mine says sodium hydrogen carbonate, but I don't see that in the app. I feel dumb, but do I just have a giant bucket of baking soda?

As far as copper, I don't see it listed on any ingredients of the things I added to the pool myself. After filling the pool in May this year, I've added:

6 tabs of chlorine over the last two months, including the two last week that weren't fully dissolved yet by the time I drained it today
4 cups of stabilizer in small doses over the first 5 days after filling
5 cups of alkaline in small doses over the first 5 days after filling
1 lb. of shock just in the last week before draining it today

None of those things list copper as an ingredient. We have copper pipes in the house though. Could that be the cause? Or maybe in the town's water supply or water mains? (By the way, I added things by cups because I have big buckets of chemicals and no way to measure doses by weight. I added a cup or two at a time over a few days to avoid overshooting.)

I might start with the tabs for now while I find some bleach. This is very helpful so far.

 

[zea3]

I'll answer your questions in red

Thanks for all the information.

I have Pool Mate Jumbo Tabs: https://www.poolmateproducts.com/_files/ugd/e6e619_25f2536db9d945da9783af6fea88361f.pdf. The label says trichloro-s-triazinetrione. Is there a way to know how much CYA is in these tablets? Is the CYA in the trichloro-s-triazinetrione itself or is it hidden in the "other ingredients"? I have a 15 lb. bucket of these tabs and there were 30 tabs, so that's 0.5 lb. each. I used the app and put in 4627 gallons (15' by 42") and say I'm adding one 0.5 lb. of "Trichlor," it says it'll:

Raise FC by 12.0
Raise CYA by 7.2
Lower pH by 0.6
Raise SALT by 9.7
There's not a way I know of to measure how much CYA is in each tablet. Manufactorers don't like to release that information. It is part of the trichloro-s-triazinetrione compound.

For the shock, mine says the active ingredient is calcium hypochlorite at 68% plus 32% of "other ingredients," and that the "minimum available chlorine" is 65%. Do I plug that into the app as "65% Cal-Hypo"? Yes If so, then 1 lb. will:

Raise FC by 17.0
Raise CH by 12.0
Raise SALT by 17.0

My stabilizer just says the active ingredient is cyanuric acid but doesn't say how much. If I put it the app as "Dry Stabilizer," a 1 lb. shot will:

Raise CYA by 26.0
Lower pH by 0.5

This is pretty neat. The only thing I don't see is an option for alkaline control. Mine says sodium hydrogen carbonate, but I don't see that in the app. I feel dumb, but do I just have a giant bucket of baking soda? Yes, that is literally all it is. A box of Arm and Hammer from the grocery store is much less expensive. You can also go store brand baking soda if you really want to save money!

As far as copper, I don't see it listed on any ingredients of the things I added to the pool myself. After filling the pool in May this year, I've added:

6 tabs of chlorine over the last two months, including the two last week that weren't fully dissolved yet by the time I drained it today
4 cups of stabilizer in small doses over the first 5 days after filling
5 cups of alkaline in small doses over the first 5 days after filling
1 lb. of shock just in the last week before draining it today

None of those things list copper as an ingredient. We have copper pipes in the house though. Could that be the cause? Probably not Or maybe in the town's water supply or water mains? (By the way, I added things by cups because I have big buckets of chemicals and no way to measure doses by weight. I added a cup or two at a time over a few days to avoid overshooting. This is where I say you shouldn't rely on pool store tests. Not only does the pool store use their "free" testing as a sales tool, they use computerized equipment that is only as good as how it is maintained. Computerized pool testing vials must be thoroughly rinsed after each use, and the computer components must be recalibrated against a standard testing solution on a regular basis in order to be accurate. The person running the tests also has to know what they are doing. As a consumer you have no idea if they are maintaining their test equipment correctly or how well the employee has been trained to run the tests. The copper levels could be interference from a previous customers water sample that was not rinsed out of the test vial correctly or from poor test calibration. Since borate and copper are not normally added to the pool we do not regularly recommend testing those levels or purchasing those test kits. When you have your own test kit you know the testing is done consistantly and you will get accurate results. We recommend an FAS/DPD drop based kit as it can test chlorine levels greater than 5 ppm and includes the CYA test that most kits do not have. There is the small HTH brand kit I linked in my first post. There is also larger kits by TF Testkits (online only) or the Taylor K2006 that we also recommend.

I might start with the tabs for now while I find some bleach. This is very helpful so far.

 

[almeida]

Thanks again. After doing the GUDAR method ("Give Up, Drain, and Refill," pronounced like "gutter"), my CYA is back down. I might take another trip to the pool store tomorrow just to have them double check what I see on my strips. I can check out what they have for test kits while I'm there. Will the kit say something like FAS/DPD right on it? I haven't found regular old bleach anywhere nearby yet, so I can see what they have for liquid chlorine while I'm at it.

I'm nervous about adding the CYA directly until I know whether I'll be able to get liquid chlorine in sufficient quantities to replace my tabs. Having never shopped for it before, I just don't know what's out there, which has me nervous. I was also thinking that I could use my calcium hypochlorite shock to raise the FC to the target range without raising the CYA, right? If you believe my test strips, I'm somewhere around 1 or 2 ppm now. If I add 0.25 lbs. of shock, I'll get 4.2 ppm. If I'm starting at 1—2 ppm, that means I'll end up around 5.2—6.2 ppm, which would put me within the target range for a CYA level from 20—50 ppm. I'm flying blind without good tests, of course, but maybe it's good enough to get started?

 

[mknauss]

Will the kit say something like FAS/DPD right on it?

It is VERY unlikely that a pool store will have the proper kit. They may have a DPD kit, but that is not what you want, no matter what they say.

calcium hypochlorite shock to raise the FC to the target range without raising the CYA, right?

Correct. It will add calcium.

I'm flying blind without good tests, of course, but maybe it's good enough to get started?

We suggest you add 3-5 ppm FC worth of liquid chlorine each day until you get a proper test kit.
Order one now. Test Kits Compared

 

[zea3]

Marty is correct. It is hard to find the FAS/DPD kits in a Pool store. It will say FAS/DPD on the label.
If you can’t find liquid chlorine you can use the cal-hypo.

 

[zea3]

Also check any big box hardware store or Walmart for liquid chlorine.

 

[Deb04]

Since you're in Mass, you can get Liquid Chlorine at Ocean State Job Lot. It's 12.5% and usually very fresh. $4.99/gallon last time I bought it, about 3 weeks ago.

 

[almeida]

Thanks for the tip about Ocean State Job Lot. I've bought all my chemicals there since getting the pool. I checked their website today for liquid chlorine and didn't see it. I'll try the store tomorrow and see if they have it on the shelf. Thanks again.

 

[almeida]

I'd been doing quarter pound doses of my Dry Tec shock to hold me over until I got some bleach. I missed a day because I was away. I'm still waiting on my test kit, so I went to the pool store and had them test it.

Free Chlorine: 1.5 ppm
Combined Chlorine: 1 ppm
pH: 7.5
Alkalinity: 88 ppm
Hardness: <50 ppm
Cyanuric Acid: 40 ppm
Copper: <0.15 ppm
Iron: 0.60 ppm
Phosphates: <250 ppb
Borate: 0 ppm
LSI: -0.74

That matches what I see on my test strips. There's only a month or two left of the season here, and I plan to drain the pool again for the winter. Unless the other values are cause for concern, I plan to just focus on the chlorine levels to get through the end of the season.

Ocean State Job Lot in Foxboro, MA, has lots of Austin's Pool Tech Shock (12.5% sodium hypochlorite). I got four gallons for $19.96. I added 24 ounces of the 12.5% bleach to raise FC by 5.6 ppm to get me to the target range (1.5 + 5.6 = 7.1). I'll add another 40 ounces to raise FC by 9.3 ppm to SLAM levels (1.5 + 5.6 + 9.3 = 16.4).

I'm hoping for the test kit today or tomorrow and then I'll have a little more visibility into what's going on without relying on the pool store. Once I get them, I'll do something like 8-24 ounces of the bleach per day to get 1.9-5.6 ppm of FC, depending on how much I'm losing. Does that sound reasonable?

 

[IceShadow]

It's hard for us to give any advice on pool store or strip testing, because we've done it before and had it backfire when it was inaccurate. Just add the 5ppm of chlorine daily - when you get your kit in, you can do the SLAM Process and get the pool cleaned up.

 

[almeida]

Makes sense. Thanks for all the help so far. The pool is looking pretty good again already, and I'm sure having an accurate test kit is going to make it even better, not to mention easier to take care of. Thanks again.