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Advice for target levels on startup after refill?


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Hi friends,

I have just taken over a 12000 gallon in ground plaster pool with terrible chemistry - here are my measurements via Taylor 2006. It's my first pool and I've been learning and haven't done much except raise the pH so far. I have a cartridge filter and solar heating, it's winter so nobody is using the pool and temp is about 53F.

CYA (using 1:9 diluted sample) is 550

CH 1300.

TA 150

pH 7.4 (I brought this up from 6.5 or below)

FC 13

CC ~0

My fill water has about 100ppm CH

I have green algae, and white scale around the tile line. I've already decided to do a complete simultaneous drain and refill using the plastic sheet method.

My questions:

If I were to deal with the algae before draining, it would require I think a shock level of at least 220ppm FC (40% of 550CYA) - is this correct and is it OK to go this high?

What target levels should I aim for during the initial weeks after the refill? Is there a chemistry I can run that will safely reverse the scaling? I'm planning to chlorinate with bleach and manage CYA separately

Thanks for any advice

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On 1/4/2022 at 2:50 PM, DiyCam said:

Hi friends,

I have just taken over a 12000 gallon in ground plaster pool with terrible chemistry - here are my measurements via Taylor 2006. It's my first pool and I've been learning and haven't done much except raise the pH so far. I have a cartridge filter and solar heating, it's winter so nobody is using the pool and temp is about 53F.

CYA (using 1:9 diluted sample) is 550

Are you sure? That is a ridiculous number. Is your test kit old?

CH 1300.

Also ridiculous.

TA 150

pH 7.4 (I brought this up from 6.5 or below)

6.5 ph will take the plaster off the walls, which might explain the high CH.

FC 13

CC ~0

My fill water has about 100ppm CH

I have green algae, and white scale around the tile line. I've already decided to do a complete simultaneous drain and refill using the plastic sheet method.

With 550 cya, your chlorine is doing nothing.

As for the "plastic sheet method", have fun with that. 😉

My questions:

If I were to deal with the algae before draining, it would require I think a shock level of at least 220ppm FC (40% of 550CYA) - is this correct and is it OK to go this high?

NOOOOOOO!!!!  The EPA will put you in jail. I'm not even sure that's possible with pool chemicals, unless you dump 1/4 of the water and refill with straight bleach.

What target levels should I aim for during the initial weeks after the refill? Is there a chemistry I can run that will safely reverse the scaling?

At 6.5 ph, scale won't be a problem, it's the opposite. Read up on plaster pool maintenance, saturation index, and chlorine sanitation.

I'm planning to chlorinate with bleach and manage CYA separately

Good plan.

Thanks for any advice

@waterbear, I think you're expertise might be needed.

My answers are in the quoted text, so open it up to read them.

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Thanks for taking the time to respond RDspaguy.

My test kit is new. I believe I'm testing correctly, fill to 7 with sample to 14 with reagent, mix 30 seconds, drop until dot disappears. Disappears well before reaching 100 for both undiluted and 1:1 samples, between 55 and 60 for the 1:9 sample. I would guess that continued algae growth even as the FC has been decaying from over 25 when I first tested supports the very high CYA reading. A hardness test using Hach 145300 matches the Taylor CH reading.

I can simplify my goals: I would like to control algae and not damage anything until I have a chance to refill and start running properly balanced water, and if at all possible I would like to avoid the need to manually scrub away the white deposits around the tile line. Any general startup advice for the new water is also appreciated.

Thanks

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Well, as my handle implies, I am a spa repair man, and know little about pools. My methods for a spa will likely be a bad choice for a plaster pool, which is why I bumped our pool chemical guru, @waterbear, for his advice.

An acid wash is the only way I know to remove scale in a pool. With a plaster pool, I would recommend you call a pro, as you can accidentally damage your plaster, and it is an extremely unpleasant and potentially dangerous job. There is no avoiding brushing. An acid wash is scrubbing with acid.

With cya that high you already know what kind of chlorine you need to affect algae. I'd drain it, acid wash it (that'll take care of the algae too), and superchlorinate at fill. Use cya to establish 30ppm, and liquid chlorine or a salt water chlorine generator to treat your pool. Keep water balanced and learn about saturation index.

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  • 3 weeks later...
On 1/4/2022 at 3:50 PM, DiyCam said:

I have just taken over a 12000 gallon in ground plaster pool with terrible chemistry - here are my measurements via Taylor 2006. It's my first pool and I've been learning and haven't done much except raise the pH so far. I have a cartridge filter and solar heating, it's winter so nobody is using the pool and temp is about 53F.

CYA (using 1:9 diluted sample) is 550

CYA test should not be run on a diluted sample. The scale for the test is logarithmic, not linear. All you really know is that your CYA is above 100 ppm!

You also said you have green algae so it will add to the turbidity of the water and the CYA test is a turbidity test. You won't be able to get an accurate CYA reading until the algae is gone.  Also, the CYA test is temperature sensitive. Make sure your sample has come to room temperature before testing your water!

CH 1300.

Only way to lower CH is by water replacement with softer water which you have with a fill water of 100 ppm. You need to drain and refill. I also suspect that you might have major plaster damage and your pool might need to be replastered. This is considered a normal maintenance with plaster pools and needs to be done every 10 years if the water chemistry is maintained, more often if it is not. My suggestion is to kill the algae (more on that in a bit) and then call a pool contractor to determine if your pool is in need of replastering. 

TA 150

Not unreasonable if the pool was being run on trichlor in a floater or feeder or if you used pH up to raise the pH

pH 7.4 (I brought this up from 6.5 or below)

Low pH CAN AND WILL damage plaster pools! No way to know how long the pH was low and the longer it is the more damage. Metal parts in the pool are also affected and that can lead to metal staining.

FC 13

CC ~0

If there is algae it is impossible to have a CC of 0 ppm. I assume the water is green. Is it a clear green (copper) or a cloudy green (algae)?

My fill water has about 100ppm CH

I have green algae, and white scale around the tile line. I've already decided to do a complete simultaneous drain and refill using the plastic sheet method.

Why plastic sheet method? IF the pool needs to be replastered the contractor will drain it. If you live in a place that does not have a high groundwater table, such as Florida, has then you can most likely safely drain about 1/2 the water or more without a problem. Repeat the drain and fill dance until CH is in range. This will also take care of high CYA. Plaster pools can pop out of the ground but it does not happen that often (mostly under flood conditions). Fiberglass pools are the problematic ones that pop out or buckle when drained unless they are properly braced.

 

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On 1/7/2022 at 1:57 PM, DiyCam said:

I can simplify my goals: I would like to control algae and not damage anything until I have a chance to refill and start running properly balanced water,

Nuke the pool! Raise your FC to about 40 ppm with bleach.For your pool this would be about 8 gallons of 6% bleach. DO NOT TRY TO TEST pH WHEN FC IS ABOVE ABOUT 15 PPM. IT WILL READ HIGH!!!!!! Pool should start clearing in about 24 to 48 hours. Watch filter pressure as dead algae gets filtered out and clean the cart if needed.

IF algae is not completely gone in a week repeat.

and if at all possible I would like to avoid the need to manually scrub away the white deposits around the tile line.

As @RDspaguysaid, an acid wash is the only way and it's best left to a pro! Maintaining proper water chemistry in the future can avoid having to acid wash frequently but an a acid wash is a normal part of plaster pool maintenance, usually every 5 to 7 years.

Any general startup advice for the new water is also appreciated.

Once you get the pool acid washed or re-plastered, follow the contractors advice for the warranty on the work done in terms of pH, TA, and CH for the first year. IF you have to get a re-plaster realize that new plaster leaches calcium and there is a constant problem with pH rise so keep plenty of acid on hand and check pH frequently! There are several different start up methods for new plaster and your contractor will determine which is best in your particular case.

If you don't need a replaster (doubtful if the pH was really low for an extended period) and only an acid wash then :

FC 4-6 ppm

CC less than or equal to .5 ppm, if higher then shock (raise FC to 15 to 20 ppm, wait for pH to drop beloe 10 ppm and retest. CC should be 0 ppm.  IF CC is still above .5 ppm repeat.)

pH 7.6 to 7.8 (Don't try to put pH low. The lower the pH the faster it will rise. )

TA 70 ppm

CH 300 to 400

CYA 40 ppm

 I strongly recommend adding borate to 50 ppm. Boric acid is the easiest way that won't break the bank. Borax and acid is the cheapest way but more work. You could opt for a commercial borate product. Make sure it's a pH neutral one (mixture of borax and boric acid)  such as Supreme Plus (Proteam) or Optimizer Plus (BIoguard) or you are just buying expensive borax and still need to add acid.  The commercial products are pricey. Boric acid is much less expensive. It will cause a slight pH drop but the pH will rise by itself over time.  Maintain borate in the 30 to 50 ppm range. Order Lamotte, Taylor, or Pool Check borate test strips online, you probably won't find them locally (I buy them on Amazon or eBay). They are much easier to read than the ones from Hach or Aquachek.

 

 

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