High CYA...How do I drain and refill?

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bluenoise

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LifeTime Supporter
Jul 25, 2007
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Alamo, CA
Hello, gang. I found this forum mentioned in another pool care forum and thought I'd join up to absorb all the great information.

I have a 20,000 gallon solar-heated in-ground plaster/gunite pool and I can't keep my chlorine levels up. At the suggestion of the forums, I checked my CYA and found it to be above 150. I didn't realize my exclusive use of dichlor and trichlor for the past few years was going to drive that up nor did I understand the ramifications. I've stopped using the solid chlorines, bought a bunch of bleach and am installing a SWG in the next couple of weeks. In the meantime, I'd like to get everything back in order. As of this morning, here are my numbers:

FC: 0.5
CC: 0
Ph: 7.2
TA: 150
CYA: 150+
Water temperature: 85 on average

The reason I've left my FC so low is that I've been draining the pool water into my yard to water the lawn and the plants (they're surviving it, so far) in lieu of running the sprinklers. The CYA number came from a test strip, so take it with a grain of salt. It may not be precise, but I'm pretty sure it's accurate in saying, "way too high." :)

So, what would be the best course of action at this point?

A. Drain the pool down and then refill it. How much do I need to drain? What are the risks (hydrostatic pressure, water table, etc.)?

B. Drain down a couple of inches and then refill repeatedly/continuous drain-refill? This wastes more water as I'm sure I'll be draining some of the fresh water in the process.

C. Live with it high while keeping FC suitably cranked up until the CYA comes down on its own due to normal water replacement for evaporation, splashing, bathers, etc? Will the SWG (Aquarite) be able to keep up or is that too much "strain" on it. I can supplement it with liquid chlorine, if needed, right?

D. We're most likely going to have the plaster resurfaced this fall after the swim season, which will require a full drain anyway. How does that affect what I should do now?

When draining, the local officials don't want it going into the storm drains due to pool water typically being high in chlorine and copper. However, mine's pretty clean of those things. I can drain into the sanitary sewer (preferred by the officials), but using to water my yard seems to be the least wasteful thing to do as long as the water is "clean" enough to not kill the plants and lawn. If I raise the chlorine to where I suspect you will suggest, it's off to the sewer for my draining.

As can be expected, I have a little bit of green algae that I've been brushing off. I run the filter pump 12 hours a day. It's a cartridge filter.

Thank you in advance for your advice!
 
bluenoise said:
Hello, gang. I found this forum mentioned in another pool care forum and thought I'd join up to absorb all the great information.

I have a 20,000 gallon solar-heated in-ground plaster/gunite pool and I can't keep my chlorine levels up. At the suggestion of the forums, I checked my CYA and found it to be above 150. I didn't realize my exclusive use of dichlor and trichlor for the past few years was going to drive that up nor did I understand the ramifications. I've stopped using the solid chlorines, bought a bunch of bleach and am installing a SWG in the next couple of weeks. In the meantime, I'd like to get everything back in order. As of this morning, here are my numbers:

FC: 0.5
CC: 0
Ph: 7.2
TA: 150
CYA: 150+
Water temperature: 85 on average

The reason I've left my FC so low is that I've been draining the pool water into my yard to water the lawn and the plants (they're surviving it, so far) in lieu of running the sprinklers. The CYA number came from a test strip, so take it with a grain of salt. It may not be precise, but I'm pretty sure it's accurate in saying, "way too high." :)

So, what would be the best course of action at this point?

A. Drain the pool down and then refill it. How much do I need to drain? What are the risks (hydrostatic pressure, water table, etc.)?

B. Drain down a couple of inches and then refill repeatedly/continuous drain-refill? This wastes more water as I'm sure I'll be draining some of the fresh water in the process.

C. Live with it high while keeping FC suitably cranked up until the CYA comes down on its own due to normal water replacement for evaporation, splashing, bathers, etc? Will the SWG (Aquarite) be able to keep up or is that too much "strain" on it. I can supplement it with liquid chlorine, if needed, right?

D. We're most likely going to have the plaster resurfaced this fall after the swim season, which will require a full drain anyway. How does that affect what I should do now?

When draining, the local officials don't want it going into the storm drains due to pool water typically being high in chlorine and copper. However, mine's pretty clean of those things. I can drain into the sanitary sewer (preferred by the officials), but using to water my yard seems to be the least wasteful thing to do as long as the water is "clean" enough to not kill the plants and lawn. If I raise the chlorine to where I suspect you will suggest, it's off to the sewer for my draining.

As can be expected, I have a little bit of green algae that I've been brushing off. I run the filter pump 12 hours a day. It's a cartridge filter.

Thank you in advance for your advice!
Click to expand...

First, get some bleach in your pool, pronto!! With a CYA of 150+ your FC should be a minimum of 12. For your pool right now, that means 4 gallons of 6% bleach.
Actually, now I see you have an algae problem so you need to shock to 33. Keep your FC at 33 until it will hold overnight and your water is clear. Brush and (clean your filter as needed - I am not too knowledgeable about cartridge filters)

Your SWG will require a CYA level of 80 or so, depending on the brand. If your water table is low enough, you could drain half and refill. CYA does not evaporate. The only way it is lost normally is through backwashing and splashout. If you close the pool dirty for the winter, sometimes that will use up your CYA.

To drain a little and refill quickly gets very inefficient. Honestly, if you plan to replaster anyway, I would just jack up the FC to the level for your high CYA and enjoy the rest of the swimming season.

There are some good links in my signature that will help you out, especially 'the stickies' and Jason's calculator.

Welcome to TFP!!
 
Thank you very much for the info!

So, with a FC level of 12+, what will that do to the swimmers? Will having such a high chlorine level cause any problems, such as bleached swimwear, red eyes, etc?

I don't think my DPD test kit can read that high of a chlorine level. How should I test it?
 
The high FC is countered by the high CYA. The effectiveness of 12 FC with 150 CYA is essentially the same as 1 FC with 0 CYA. Should not hurt your swimmers a bit. Rinse off upon exiting the pool, just to be sure!

You can order an FAS DPD test through TF Test Kits (linked in my sig), or probably get one at your local Pool store. I think they read up to 50 FC, and will check TC and CC's also
There is a dilution method that can help you until you get a better test, but I am not sure it works with DPD tests... It is not too accurate in any case, but better than nothing.
 
12 ppm FC with 150 ppm CYA is equivalent in disinfecting chlorine concentration to 0.1 ppm FC with no CYA so is far less than found in indoor pools. My wife's swimsuits degrade (rubber wears out) in just one winter season of swimming in an indoor pool with around 2-3 ppm FC and no CYA while in our own outdoor pool with 3-6 ppm FC and 30 ppm CYA there is no degradation whatsoever. You should find no noticeable difference from being in the water.

Out of the water, there will be more chlorine available in your drying swimsuits so though the rate of bleaching won't be any faster, the potential for bleaching as the water evaporates *might* be higher, but I do not know if this is true. If you rinse off after getting out, there should be no problem. Other pool users with similar high FC high CYA levels have not reported any bleaching or eye stinging problems.

Richard
 
Very good. I picked up six jugs of Clorox last night at Costco. It looks like I'd better pick up another trunkload!

Will my new Aquarite SWG (ordered and on it's way) be able to keep up with the 12+ ppm load or will it need some help from the bleach?

Thanks again!
 
The very high CYA level will prevent the sun from destroying as much chlorine as it would at a lower CYA level. I expect that the SWG will keep up just fine once you get to the initial level.

For a 50% water replacement continuous filling and draining, holding the water level more or less constant, only uses 10-20% more water and it usually goes more quickly.

Living with very high CYA levels is possible, but there are many challenges. The most significant is that at the required FC levels the PH tests tend to be off. The Taylor PH test is listed as good to a FC level of 15, but many people have problems at 10 or above.
 
OK, so perhaps my best course of action will be to pick up some more bleach and shock the pool tonight. I will also do a little water replacement each evening for the next couple of days (unfortunately, I have to go out of town Friday and I get home Monday night). It seems even a little water replacing will help bring down that CYA level a touch.

Once I get the SWG up and running, I can keep up with the water replacement while maintaining the proper salt level. Over time (until we do the drain this fall for the resurfacing, if we can justify the expense), the CYA should drop.

Sound reasonable?

Regarding the shocking: If I blast it with enough bleach to bring it up to the 33 ppm, how long can I expect it to hold at that level? Will it just drop quickly as it does its job or will the high CYA help maintain a higher level? I'm trying to calculate how much bleach to buy in addition to the amount needed for the shock.
 

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That makes sense. As far as I can see, there is a patch of green near the wall connection where the Polaris hose attaches. It's in the little crevice, so I can't quite get it with my brush. Total visible algae is probably about 1-2 square inches, but there could be more hiding somewhere like the filter. The water is still sparkling clear, so (hopefully) it won't consume too much of my chlorine.
 
I just blasted the pool with over 10.5 gallons of Clorox bleach and will let the pump run for the next 24 hours. I'll check the FC in the morning, but my kit can't handle that high (hopefully) of a chlorine level. If I dilute the pool water 10:1, will I get a decent ballpark reading if I then multiply the test result by 10? Should I take a reading of my tap water and use its FC reading in some calculations? I figure the tap water's FC reading is probably pretty insignificant compared to the targeted 33 ppm reading I'm hoping to get in my pool.
 
Diluting much past 2 or 3 to one with the OTO test I think you have is incredibly innaccurate. Your best bet is that you calculated correctly (sounds like you did) and the results will be predictable. It also sounds like you don't have a full-blown pea-green pool so you shouldn't consume the chlorine too quickly.

My guess is your test will go to 5ppm so you might try a 3-1 dilution and get in the ballpark to measure up to 15. Yeah, your tap water is most surely less than 3ppm or so.....I'd disregard it. With the high CYA in your pool, it'll be helpful to you to get the FAS/DPD test for chlorine which will measure super high chlorine.....50+ and it's accurate.
 
Dilution with tap water will reduce the accuracy so far that you might as well not bother. You really need to use distilled water. The highest dillution I would try would be four to one, but as duraleigh says it gets less and less accurate and at some point guessing becomes a better method (which is to say it becomes useless).

The full FAS-DPD test is the only thing which will measure chlorine levels in the range you are dealing with. This is another one of the problems of dealing with high CYA levels. TF Test Kits has a FAS-DPD tester available without the rest of the kit, and Taylor sells one as well. But really getting a full high quality test kit is the best investment in your pool you can make.
 
I just checked the pool this morning and here are the results. My test kit is the Taylor Deluxe DPD Test Kit.

FC: 5.0
Ph: 7.2
TA: 160

I thought the DPD test would "bleach out" at FC levels over 10 ppm. If so, does this mean I'm truly down to 5 ppm? Is there any harm in assuming I am and adding enough bleach to go back up to 33? In other words, if my FC is actually at, say 20, would increasing it by 28 have any negative effects besides wasting bleach?

The algae spot was still there, so I brushed it out with an old toothbrush. Now, I don't see any algae and the water is still clear.

It seems my TA went up by 10, too. Is this a byproduct of the shocking I am doing or just an error in my readings?

ETA: I just did the test again by diluting with tap water 3:1. I got a reading just over 1 ppm. My tap water alone registers no measurable chlorine (test stays completely clear).
 
DPD will read at one end of the scale or the other if your chlorine is very high. A reading in the middle is reliable.

The TA test is +-10, so it is probably just the usual impercision in the test and not any change in your water.
 
I'll pick up a FAS-DPD kit with CYA test today. I'm overdue anyway. That should give me the readings I need to really deal with this situation.

Since I am going to have to leave the pool alone until Monday night, what should I do before I go? Should I pour in a bunch more bleach? I figure the amount will depend on my FC levels tonight, but I'm wondering if that will carry me through the weekend.
 
I just got home, so I tested my FC level again. With the 4:1 dilution, I came up with ~8 ppm. So, I tried a 2:1 dilution and also came up with 8. I guess it's 8. Pool Calc tells me to add 5.7 jugs (1.42 gallons each) to get it back up to 33, so I added 7 jugs. In the morning, I'll test again and hit it with another overage before I have to catch my flight.

The good news is that I had seen some algae inside the float on the Polaris, but it's gone now. Woo! I'll keep hammering on it for the next 24 hours.
 

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