High CYA -- water change advice

[Dirk]

I've been replacing the water in my IG pool for the past 5 days to bring my CYA down significantly. Per PoolMath, I had to replace 78% of my water, or approximately 24,000 gallons.

Since the new water is much cooler than the water in my pool, I ended up adding water in the deep end and pumping water out on the shallow end (with the pump sitting on the top step). It worked out quite well and was automatic once I got the inflow to match the outflow.

How do you determine each time how long the process goes for? How do you know when you've exchanged enough water to suit your CYA level?

 

[Grape Ape]

How do you determine each time how long the process goes for? How do you know when you've exchanged enough water to suit your CYA level?

I imagine you could get a pretty good idea of your hose's fill rate using your water meter and a stopwatch (there is probably an app for that on your phone).

A five gallon bucket and a stop watch app should also work.

 

[wilafur]

How do you determine each time how long the process goes for? How do you know when you've exchanged enough water to suit your CYA level?

Should have been more specific. I timed the pump rate based on how quickly it filled a 5g bucket. Based off that, the math indicated it pumped approximately 200g per hour. This meant I needed to pump/fill for approximately 5 full days to exchange 24,000g. Hope that clarifies things.

 

[Dirk]

Should have been more specific. I timed the pump rate based on how quickly it filled a 5g bucket. Based off that, the math indicated it pumped approximately 200g per hour. This meant I needed to pump/fill for approximately 5 full days to exchange 24,000g. Hope that clarifies things.

rob, so there you go. You've got a few methods to figure out how much water you're exchanging for the no-drain method:

- use your house meter if you have one

- put a flow meter on your hose

- or use a bucket to figure out your hose's flow rate and count the hours/days

That's probably in the order of accuracy, depending on how much you spend on a flow meter if you go that route. But remember, there will be some mixing, so no measuring trick is going to give you perfect results in terms of actual chemical level dilution. You measure flow to get close, then you test your water to see how you're doing. Lather, rinse, repeat...

 

[s_vidden]

Yes, in a quick re-read, I can't find if the OP's pool is IG or AG. His concern about how much to empty led me to believe it is IG. Which inspired my comments. Pardon if I got that wrong...

s_vidden, your comment about not needing a flow meter and determining the amount of the exchange with dimensions makes sense if the OP is going to drain and refill. If he's going to exchange as I suggested, I think he would need a flow meter, at least to get close. His water level won't be dropping, so there's nothing to measure! The exchange won't be exact, and some mixing will occur, but a flow meter would keep him in the ball park.

Good news, rob42, whether you need one or not, you've probably already got one, if you're on metered water. You can use the house meter out by the street. Impose a ban on showers, laundry, dishes, etc. Go out to the street and take a picture of the number on your water meter. Start the exchange and keep an eye on the meter for when you hit your mark. The picture is in case you forget the starting number (something I would do in like five minutes!!).

You'll be hopping back and forth to maintain the water level and eye the meter. Balancing water being siphoned out vs water coming in. Then checking the meter for your target number (determined with a little math, adding the desired gallons to exchange to the original meter read). EZPZ. Meanwhile, the rest of the family will be lounging inside because they've just been given the day off: no laundry, no dishes, no washing the car, etc. It's a win-win!!

DIRK,
The exchange method makes sense now. I was envisioning the slower process of draining and refilling separately. I have also measured the flow rate of my outside hoses by measuring the time it takes to fill a 5 gallon (pre-marked) pail or larger vessel as long as it is marked at a predetermined level. Run the test 3 times and take the average. He will have the flow rate of his hose(s) and can easily calculate that flow rate in gallons/hour. That would get him very close with out the fancy metering, especially if banning water usage in the house just isn't going to happen. LOL. Just some red-neck engineering!! Cheers!

 

[Dirk]

DIRK,
The exchange method makes sense now. I was envisioning the slower process of draining and refilling separately. I have also measured the flow rate of my outside hoses by measuring the time it takes to fill a 5 gallon (pre-marked) pail or larger vessel as long as it is marked at a predetermined level. Run the test 3 times and take the average. He will have the flow rate of his hose(s) and can easily calculate that flow rate in gallons/hour. That would get him very close with out the fancy metering, especially if banning water usage in the house just isn't going to happen. LOL. Just some red-neck engineering!! Cheers!

Yep, that'll work just fine.

 

[rob42]

So, I had no access to a flow meter (the house meter being of the "buried under a pentalobe plate in the front yard" variety", so I just did some water exchange on Friday to make a start. I pumped out up high on the shallow side and filled with a garden hose zip-tied to a pole at the low point of the deep side. Ran for a business day or so.

Readings this morning:

pH: still high -- top of the scale? 8.2?
FC (drop test): 7.5
CYA: 90
TA: 180
CH: 50

I think I need to bring the pH down. I was sure the tap water would do it, but it didn't.

Is there a more accurate test for pH? I guess if I am out of range, that's all I need to know?

Thanks.

 

[ajw22]

Assume your ph is 8 and use PoolMath with target of 7.2 . Drop PH down and retest. Repeat as needed until you get PH test results in the 7s.

 

[Dirk]

Add muriatic acid to bring your pH down into a testable range. I would enter 8 in PoolMath and set the target for 7.5. Add that recommended amount of acid. Wait an hour of so, as you circulate the pool (run the pump). Repeat until your pH is in range of testing, then add the last dose of acid to reach your desired pH target.

Most pH tests only go up to 8 or so (some a bit higher, some a bit lower). I don't think there are any that go up beyond that, not that you get in a pool testing kit. The trick, of course, is to never let it get out of range, but sometimes it just does...

- - - Updated - - -

AJ beat me with good advice. The only reason I wouldn't target 7.2 is: unless you're very confident in your water volume, then you could overshoot and get below 7s if your volume number in Pool Math is not accurate. You used a ~ when citing volume, so you might play it safe. Once you're past this challenge, we can share some ways to fine tune your volume number.

 

[ajw22]

AJ beat me with good advice. The only reason I wouldn't target 7.2 is: unless you're very confident in your water volume, then you could overshoot and get below 7s if your volume number in Pool Math is not accurate. You used a ~ when citing volume, so you might play it safe. Once you're past this challenge, we can share some ways to fine tune your volume number.

I figured the higher than 8 will offset any pool volume error.

If in doubt of pool volume then you should add 1/2 to 2/3 doses of PoolMath amounts and see if your pool is responding as expected. Always better to sneak up to the target with a few rounds then overshoot it.

 

[Dirk]

I like the “sneak up on it” approach. OP is new to his pool, his kit, and TFP. No harm in taking it a bit slow. This will all be second nature in short order...

 

[rob42]

I got some more "pool store" water analysis.

They say the pH is 8, and it might well be, for all I know.

They say TA is 120. I drop-tested it twice and it came out exactly 180 both times.

They say that my CYA has not come down hardly at all -- 129 -- and I hope they are wrong about that. The CYA test in the kit is another one that doesn't seem very deterministic. How bright is the light? How good is my eyesight, etc. I will try the diluted test and see if that makes any sense.

I *do* need to get a flow meter, so I know what to expect. If i need to change ~70% of my pool water, that's probably even more hours of this process than I had imagined. I will do the stopwatch test on a 5-gallon bucket, and probably get pumping again.

I bought some PH down, but no point in treating it and then pumping it out.

 

[ajw22]

They say that my CYA has not come down hardly at all -- 129 -- and I hope they are wrong about that. The CYA test in the kit is another one that doesn't seem very deterministic. How bright is the light? How good is my eyesight, etc. I will try the diluted test and see if that makes any sense.

Some people who have trouble with the CYA test have bought the R-7065 CYA Standard 50 ppm (2 ounces)

Practice with that and you will see what CYA 50 looks like in your tube under your light.

 

[rob42]

Some people who have trouble with the CYA test have bought the R-7065 CYA Standard 50 ppm (2 ounces)

Practice with that and you will see what CYA 50 looks like in your tube under your light.

I am draining more. I did the 5-gallon bucket test and found out that my pump is only removing 300 gallons an hour. (I probably only changed ~2,000 gallons last time.) I think the fill is slightly faster. So, I am going to drain for 10 hours, drain-and-fill for 10 hours, then fill to the correct level. Run the pump for an hour, test again, then adjust for pH.

I think that if I do the CYA test, and then the 50% diluted CYA test, and they somewhat agree, I will feel better about the results.

 

[Dirk]

Trust your own testing. Eventually, you will need to let the "comfort" of the pool store results go, best to do so sooner than later. The notion that they should know what they're doing, they must have better methods, better equipment, etc... all false hope. Your results will very likely be better than theirs even now, and after a few days of testing your results will definitely be better than anyone else's. (Assuming you have one of the two "approved" test kits, which are as accurate as any pool needs.)

ajw22 gave you some solid advice about getting a hold of the CYA sample. That will definitely improve your confidence about your CYA testing. And by the way, this is not a newbie thing. The CYA test blows. No suger-coatin' it. Most of us hate it. Everyone struggles with it. No one here actually knows what their CYA level is (the degree of accuracy of the CYA test is pretty much the worst in the kit)! Even for those of us who have done it a lot, it still teeters between science and subjectivity. You do the best you can, then back up what you think you know about your CYA level with how your FC level maintains. I'm not saying the test isn't important, or that you shouldn't strive to do it the best your can, you have to. Just don't sweat it.

 

[rob42]

I drained about 6,000 of 17,000 gallons -- more of a schedule issue than anything else, as this took 20 hours of supervision. I think my CYA is down to 80 or so. I'm still lousy at the test, and I am seldom around in full sunlight! I can do another change later, or just keep the FC up for the rest of the season, right?

The pool store talked me into some shock to lower my CC, and now my FC is at 20.5 (20 hours after application). What *is* the highest FC one can swim in, anyway? I guess this will take a few days to go down. TA is 110. CC is essentially zip.

I corrected the high pH, and got it into a good range, but after the shock it is high again, so I just corrected it again.

You are right. Enough with the pool store. Apparently there is no relationship between CYA and required FC levels. I learned that from the pool store.

 

[ajw22]

What *is* the highest FC one can swim in, anyway? I guess this will take a few days to go down. TA is 110. CC is essentially zip.

You can swim in FC below the shock value for your CYA level according to [FC/CYA][/FC/CYA] For CYA 80 that would be 31.