My Green Pond Challenge

[Cinquefoil]

As a volunteer at our neighborhood pool (165K gal, treated with 12% bleach and muriatic acid) I have learned enough over the years to be dangerous. But if you know a little more than the next guy you are labeled the expert around here, which is how I was invited to walk in to this situation at a friend's home.

His pool... 20,000 gal, sand filter, green with visibility to about 8 inches below the surface. My Taylor kit found no Cl, pH=7.3, TA=110, CH=230, and CYA a whopping 130 ppm. Lots of empty dichlor, trichlor, and algaecide containers from A&S Pool. He had just shocked the pool for the umpteenth time to attain 10 ppm Cl. Water level was above the skimmer. He said it has been green for a month and was not getting better.

My first thought was drain and fill to lower the CYA, but that's not practical for him. My second thought was that the high CYA was preventing treatment and possibly giving false test kit readings. And that I didn't want to add anything that would raise the CYA even more. So we put away all the white containers and went to the store for some gallon bottles of 6% bleach.

My calculations show that 3 gallons of bleach should raise Cl by 10 ppm, so I added 6 gallons on top of the Super Pool Treat he had just done with hopes of attaining 30 ppm overnight. Backwashed three times during the day which lowered the water to mid skimmer and improved flow rate significantly. He claims that he can now almost see the bottom -- some improvement --though I'm not sure I agree. But all the floating bugs are now dead.

Tonight I added 9 more gallons of bleach and hope to see some change in the morning.

Am I on the right track here? He's a bit in disbelief that my $2.00 bottles of bleach can do better than his hundreds of dollars of pool store chemicals. So my credibility is on the line for results. My intent is to add 9 gallons of bleach each night until the green turns brown. Any thoughts on how long that will take? Then reduce the bleach to 3 gallons each night while brushing, vacuuming, backwashing, and filling until his teen is exhausted from the work. And hoping that at some point the test kit readings will fall in line.

Is this a good plan? Anything to do differently?

Thank you for the sage advice I'm sure will follow.

 

[duraleigh]

Welcome to the forum.

My first thought was drain and fill to lower the CYA, but that's not practical for him.

Your first thought was a good one. I would make no further attempt to clear the pool until the CYA was lowered to 40-60ppm.

The CYA of 100+ will make pool maintenance a continual headache and it won't get any better until you/he bites the bullet and lowers the CYA.

 

[Casey]

I agree with duraleigh!

There is no way you can keep the bleach going withough dumping God Awful amounts of bleach every night. You'd spend more on bleach than fresh water by July!

I say, accidently drain it below the skimmers a few times and filler back up! Tell him there was alot of Crud in the filter or something! That high of a CYA is his main reason why he can't combat the algae!

While you're at it, send him to pool school! You should read up on it too. Take special note to the Chlorine/CYA chart!

 

[Lershac]

The pain will continue until the CYA has been lowered.

Drain as much as you can and refill. Repeat until the CYA is down to 50 (or lower!). The tackle the ookiness.

 

[Lershac]

But working the teen to death is a good idea, it keeps em out of trouble!

 

[Casey]

But working the teen to death is a good idea, it keeps em out of trouble!

You can still work a teen to death with a low CYA.

 

[JasonLion]

You have a couple of problems. It is almost impossible to measure CYA levels over 100 accurately. If you know what the CYA level really is, it is possible to clear the pool even with a very high CYA level. However, problems will continue after the pool is cleared because of the high CYA level.

Clearing the pool is probably a waste of time because there will still be future problems, as others have mentioned. But if you want to continue trying to clear the pool, you should aim for a shock level of 40. That means first testing the current FC level and then adding the correct amount of bleach to bring it up to 40. Simply adding several more gallons without testing could result in a level that was too low or too high, neither of which would be good.

 

[Butterfly]

Hi Cinquefoil,

I kinda think you already knew your answer before you posted

Ditto on the drain/refill dance.

Welcome to the forum

 

[PaulR]

You can run the CYA test on a sample that's 1/2 pool water 1/2 tap water, and double the result, to extend the range of the test. Some loss of accuracy but it's not all that accurate to begin with. Will give you a little better handle on how bad it is really.

Assuming you do manange to clear the pool without draining, your friend will be in high-CYA maintenance mode which will require weekly doses of polyquat 60 until the CYA comes down.
--paulr

 

[Cinquefoil]

Thank you for all the quick responses. Yes, I had an inkling what was needed but it very much helps to have your guidance and reassurance.

I'm a hero. At least for today. We started treating Sunday night and friend woke up on Tuesday to find the green totally gone. First time since April. And he has a large supply of empty bleach bottles to recycle. Now the pool is bright blue and cloudy. I'm assuming a lot of that is dead algae waiting to be vacuumed and filtered out.

It was a small challenge to convince him to replace the water. First night he disposed of two inches, leaving it just below mid skimmer. I talked with him about the cost of water versus the money for chemicals he would need. Last night I stood by as he lowered it to the vacuum port through a combination of vacuuming, backwashing, and pumping to waste.

I ran an extended CYA test with half tap water and half pool water. Still way above above 100 ppm.

This next part is funny. I did tell him that once the algae was gone to take a sample back to the pool store for another test. They use a computerized system that gives a nice printout... and saves the reagents I borrowed from my neighborhood pool. So his wife takes in the sample. They tell her the chlorine is too high and pH is too low. They sell her soda ash, oxidizer (which I later learn is KMPS), cal hypo, phosphate reducer, and an expensive blue brightness enhancer, which I think is a floc agent. But they won't give her the printout because they say the numbers are so out of range that it would be meaningless. I tell him to add these items to the growing pile in his basement. If you think any of them might be helpful, let me know... they are already paid for and not returnable.

Plan for tonight:
- Vacuum, backwash, and pump water to lower the level to the vacuum port again, then refill.
- Allow chlorine to lower itself to 10 ppm, then add bleach as needed to keep it there.
- Hope that he sees the bottom; else I will be pressured to add something, maybe the floc agent?

Still on the right track?

 

[duraleigh]

Still on the right track?

If the current CYA level is still over 60, you are not. It sounds like the pool is still over 100ppm.

 

[Cinquefoil]

Yes, CYA still way over 100. Can only dump as much water each day as he will let me. So I plan to keep the bleach levels up to compensate until CYA comes down.

Recognizing the futility of extrapolating the chlorine/CYA chart for CYA over 100, would these seem like reasonable targets?

CYA Min FC Target FC Shock FC
20 2 3 10
30 2 4 12
40 3 5 16
50 4 6 20
60 5 7 24
70 5 8 28
80 6 9 31
90 7 10 35
100 7 12 39
110 8 13 43
120 9 14 47
130 9 15 51
140 10 16 55
150 10 18 59

 

[PaulR]

A more elaborate (but I think less readable) version of the Pool School chlorine/CYA chart is in this post which also gives these formulae:

NOTE: A reasonable approximation to the above table is the following:
.... "Min FC" is 7.5% of the CYA level
.... "Target FC" is 11.5% of the CYA level
.... "Yel/Mstrd Min" is 15% of the CYA level
.... "Shock FC" is 40% of the CYA level
.... "Yel/MstrdShock" is 60% of the CYA level.

For example, CYA 120 would produce Min=9, Target=14, shock=48; CYA 150 would be Min=11, Target=17, shock=60.

So you were close!
--paulr

 

[JasonLion]

My Pool Calculator will calculate recommended FC levels based on your CYA level for very high CYA levels. You don't really need shock levels as high as chem geek's formula says at extreme CYA levels.

 

[Cinquefoil]

Wednesday evening update:

Pool is clearer. Can see the bottom in the shallow area.
Chlorine still well above 10 ppm.
CYA still well above 100 ppm (even with half sample).
Added no chemicals today.
Backwashed, vacuumed entire pool to waste.
Lowered water roughly 8 inches and refilled.
By my calculations we are exchanging about 2500 gallons per day.

 

[PaulR]

By my calculations we are exchanging about 2500 gallons per day.

That's about 1/8 of the 20k gal pool. (7/8)⁵ = 0.51 so you'll need to do that 5 times to reduce the CYA by about half. Just so you know where you're headed.
--paulr

 

[Cinquefoil]

Friday night update:

Pool is much clearer. Can easily see the bottom in the nine-foot area.
Chlorine still well above 10 ppm.
CYA still above 100 ppm (even with half sample) but coming down.
Added no bleach or chemicals since Monday.
Backwashed, vacuumed entire pool to waste. Appears all remnants of dead algae are gone.
Dumped a lot of water. We exchanged over 10,000 gallons by now. Pool was still filling tonight.
pH is 7.1 - 7.3, TA = 40.
Plan is to test again in the morning and dump more water.

 

[Gooserider]

Note that by doing only partial dump and refills you are wasting a great deal of water...

Assuming you are replacing 5% of the water each day - the first day you replace 100% high CYA water, the second day you replace only 95% CYA water, and 5% of the fresh water that you added the day before. The third day you will get about 90% of the original CYA water, and 10% of your replacement water, etc... The math doesn't work out quite that simply, but it's a good first approximation...

You will end up replacing far less water to get to your objective if you pump out at least as much as you would need to replace to get from your current level to the target level in one go and refill, as opposed to doing just a bit at a time... If anything I would even pump out MORE than I had estimated as needed, as it is far easier to bring up the level if you get it down to far than it is to lower it...

Gooserider

 

[PaulR]

Note that by doing only partial dump and refills you are wasting a great deal of water...

But sometimes that's what you have to do, for various reasons, the biggest being a high water table. Cinquefoil hasn't specified why the friend doesn't want to replace much water at a time.
--paulr

 

[Cinquefoil]

Dumping sufficient water is more a psychological barrier than anything else. But we achieved success anyway. It's just taking extra days. Pool was clear to the bottom of the deep end by Saturday morning, and his family swam all weekend (and invited us over this evening for a swim and barbeque). Backwash is very clear.

Friend took a sample to the pool store on Saturday with these results (their recommended range in parentheses):

FC = 8.1 (1.0 - 3.0)
TC = 8.1 (1.0 - 3.0)
CC = 0.0 (0.0 - 0.2)
pH = 7.0 (7.4 - 7.6)
CH = 90 (225 - 375)
TA = 46 "with stabilizer correction" (100 - 130)
CYA = 80 (30 - 150)
Copper = 0 (0 - 0.2)
Iron = 0 (0.0 - 0.2)
TDS = Not Run

Pool Store prescription: 25 lbs pH stabilizer (I think they mean soda ash) and 50 lbs hardness control (calcium chloride). And something to reduce high phosphates. Wow.

And they said not to use the pool until chlorine was within the ideal range (<3.0). And they said the CYA is OK.

With my newly acquired credibility, I told him to disregard all this and add on Saturday whatever baking soda he had left. Because somewhere I came to believe that good TA was the key to most everything else. Then tested with my Taylor 2005 on Sunday night with these results (my recommendations in parentheses based on numbers from TFP and Taylor):

FC = 4.0 (3.0 - 7.0, leaning toward 7.0 - 10.0 until CYA comes down)
TC = 4.0 (identical to actual FC)
pH = 7.2 (7.4 - 7.8, ideally 7.6)
TA = 110 (80 - 100)
CYA = 100 (30 - 50)
CH = 160 (50 - 300, but don't really care because he has a vinyl liner)
SI = -0.4 (raise pH to drive this to 0.0)

My prescription for Monday, with some help from Jason's pool calculator:

Dump more water, as much as I can convince him to do.
Add 1.5 gal 6% bleach to ensure no more algae, driving toward 9.0 FC.
Add 2 pounds of soda ash to raise pH a little.

Will probably have to dump more water on Tuesday as we keep driving down CYA.

Any objection to this approach?