Where do I start

[mxdad777]

I recently bought a house with a 28 year old in-ground plaster pool. The pool hadn't been neglected, but it hadn't been kept up very well either. I recently cleaned up the pool tile (glass bead blaster), cleared up the slightly green and cloudy water (lots of granular shock and chlorine pucks in 3 floating chlorinaters). I also recently installed a new Pentair VS pump, Hayward salt system, booster pump and replaced all grids in the DE filter. I now have the water looking crystal clear, but it's not in balance. I live in the country and have a private well. My pool has an auto fill and it is connected to the soft water system in the house, so any fill water is after the water softener. With the old test kit I had, I knew the ph was high (8.0) and the TA was high (400) but that's all I knew. Over the past two weeks I have added 10 gal of acid and have also aerated the water off and on. Today I got my new test kit and have the following results to report.

FC 5
TC 5
CC 0
PH 7.3
TA 200
CH 350
CYA 120
Salt 3400
Water temp 68 deg

For reference, below is what my tap water in the house is. Same source that fills the pool.
FC 0
TC 0
CC 0
PH 7.4
TA 525
CH 50
CYA 0

When I installed the salt system the FC was 8 due to the floating pucks and shock. I originally had the salt system set at 30% but shut it off last week to bring the chlorine down. So based on all of this, where do I go from here to get my pool in balance?
Thanks in advance for any and all help.

 

[jblizzle]

I think it is going to be a little difficult to deal with the CYA level as high as it is as the recommended level for SWA is 70-80. Only way to fix that is through water changes. (All those pucks and granular chlorine did not do you any favors)

I know you noticed poolcalculator being down {well it is back now} ... here is a link to some recommended levels:
pool-school/recommended_levels

The other tricky part is going to be dealing with your TA levels (ideal is 60-80). Having this high is going to generally pull the pH up. There is a method to lower the TA as shown in Pool School, but it may take a long time and a lot of acid (just saw it looks like you are already doing this ... and apparently it is working )

With your high CYA level you need to stay up above 6ppm on your FC with the SWG (without the SWG it would be 9-15)

 

[mxdad777]

So the Pool Calculator says I need to do a 33% water change to lower the CYA to 80. Should this be done a little at a time over a few weeks, or should I do it all at once? I'm not too thrilled about draining 12,000 gallons of water, but I guess I have to do what I have to do. Because the TA in my fill water is 525, I guess I can expect my TA to sky rocket again. Sounds like I just wasted a lot of muratic acid over the past two weeks trying to bring my TA down.

 

[jblizzle]

How did you come up with a cya of 120? Test goes to 100?

Did you use half pool and half tap water? Might be worth trying if not.

If it is 120 then a 33% water change would drop it to 80. 50% would drop to 60 etc.

You might see if your swg can handle it ... although would hate for you to keep lowering the ta just to maybe have it rise again with a water change later.

 

[mxdad777]

How did you come up with a cya of 120? Test goes to 100?

I just estimated where 120 would be based on the marks.

What do you mean by half tap water and half pool water? Is this so it stays on the scale and then I would just double the test results?

 

[jblizzle]

You got it. Tap water has no cya in it so you do not need to use distilled water. Just start with 50/50 pool and tap and then double the result.

You loose a bit of accuracy but better than guessing off the scale.

You can pour it back and forth a few times to see if you always stop at the same place.

Also note you are best to do the test in indirect sunlight per the directions.

 

[mxdad777]

So should I drain 33% to 50% of the water all at once, or should I change out the water gradually over a few weeks?

 

[jblizzle]

Retest your cya using the 50/50 method to be sure you are around 120 first.

It will take less water if you change everything you need to change at the same time. Any idea where you ground water table is?

 

[mxdad777]

I'll do the 50/50 test this afternoon when I get home. I didn't want to do it last night in artificial light.
I'm not sure where our water table is (I think around 25') but my next door neighbor completely drained his pool about 4 weeks ago to do some major cleaning and didn't have any problems. If my level is at 120, my plan is to drain 2 feet and fill, drain 2 feet and fill. I have an external sump pump that I can drop in the pool. I was going to measure the output (GPM) of my pump and then calculate it out so I know how much I am pumping out per hour. Once I get close to a 30% water change, I will start testing the CYA and keep up the process until I get to 70. Does this sound logical, or is there a better way? Once the CYA is at 70, I'll start attacking the TA problem again which I'm sure is going to go way up considering what the TA level in my tap water is.

 

[jblizzle]

Sounds like you neighbor was a good guinea pig so your should have no issues with the water table.

The least amount of water is used if you can do the entire replacement in a single drain and fill. If you do smaller changes, each subsequent change is lowering the CYA by a smaller percentage.

For example, assuming CYA of 120:
A single 41% water change would take you to about 71ppm
It would take 5 10% water changes to get you to the same 71ppm ... so it takes about 9% more water this route.

Not really a big deal either way ... what ever you are comfortable with. You will also reduce the level quicker if you are not filling the pool at the same time (although there are ways to accomplish this ... but given your lack of water table issues, bot something you need to deal with).

 

[mxdad777]

Well, it's worse than I thought. I just did the 50/50 test and my CYA is somewhere between 180 and 200. If I fill the vile until I can't see the black dot at all it's 200. If I go by where it starts to disappear and is very hard to see it's 180. So either way, I'm looking at a big water change which is going to put my TA through the roof. I guess I don't have an option though, do I?

 

[jblizzle]

Only other route to remove the CYA is though paying a company to come out and do a Reverse Osmosis treatment on your pool. This will also reduce your CH and apparently the TA some as well. See this post:
to-drain-or-not-to-drain-t41304-20.html#p340980

 

[mxdad777]

I just dropped my 60 gallon/minute pump in the deep end. I figure in about 6 hours I can start the refill. Man it sure is hard watching all that water go to waste. Not to mention all the salt and acid I added in the past 2 weeks. Oh well, it should all work out in the long run.

 

[mxdad777]

One last concern.....seeing that my plaster is 28 years old and is starting to look a little rough, do I have any concerns with the plaster popping off or any other issues with less than half the water in the pool? We plan on replastering the pool, but not for a year or two.

 

[mxdad777]

I had a big brain fart earlier! I was concerned about having my pool half empty because I heard at one time that it could cause a problem with older plaster pools if the plaster was exposed. So as I have been pumping out 60 gallons of water per minute I have been adding 40 GPM with 3 garden hoses. Duh! It didn't dawn on me that I would be pumping out some of the good water that I'm putting in my pool along with the bad. So anyway, I just turned off the fill water, but now I have no idea how much "bad water" has been removed. In round numbers over the last 3 hours I have pumped out 11,000 gallons of water (good and bad mixed) and have pumped in 7,000 gallons of good water. Any guesses as to how much more water I need to pump out to equal my 65% (23,000 gallons) of water change? Boy I feel stupid!

 

[jblizzle]

If you were pumping out at the deep end and adding at the shallow you may have pumped out less good water than you think.

Hard to guess how much more to pump out though. Maybe just aim for a little more than you planned and that should get you in the ballpark.

 

[mxdad777]

Okay...after refilling pool and circulating the water for the past 4 hours, here are my new numbers. I don't know the salt number yet, I figured it would take a day or two for my salt system to give me a proper reading. I think I will take a sample down later and see what the pool store reads my salt at.

FC 3
TC 3
PH 7.6
TA 325
CH 310
CYA 75

As I figured, the TA is way out of whack. So I'm assuming my next step is to start adding acid until the PH drops to 7.2 and then aerate to bring it up and keep this process going until I get my TA to around 70. Does this sound right, or is there something else I should be doing too? And what's the best way to add the acid to bring down the TA? In the past I would dump 2 gallons around the edge of the pool with the pump off. After 4 hours, turn the pump back on, wait 2 hours and then check PH and TA. Is this the correct way to do it?
Thanks again for all the help.

 

[jblizzle]

Wow ... good job on guessing the right amount of water to drain. Got the CYA dead on

May want to add a little bleach and/or bump up the SWG a bit (if it is actually running). For CYA of 75, with SWG you want to keep FC between 3-5ppm.

It is not recommended to add the acid the way you are doing it as it will just pool on the bottom and potentially start to damage your plaster ... this is known as the "slug method" and has been proven do more harm than good. {EDIT see the last paragraph in the Lowering Total Alkalinity page in Pool School for a link to a paper discussing this}

You want to pour the acid slowly right in front of a return preferably in the deep end with the pump on so the acid mixes pretty quickly. Dose to get down to 7.2 and then then aerate to bring the pH back up ... just like you had been doing.

 

[mxdad777]

I read the article in pool school about lowering TA. It states that you can provide aeration with a SWG. ("Aeration can be provided by a SWG, spa jets, waterfall, fountain, return pointed up so it breaks the surface, air compressor, kids splashing, rain, etc.") I have been using a modified external pump, how do I use my SWG to aerate the pool? I just added acid to the pool as per pool school instructions, so I will be needing to aerate soon.

 

[jblizzle]

The SWG tends to raise the pH just from use ... so I guess that is the aeration mentioned.

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