Tarp method in-place water replacement

carlos31820

LifeTime Supporter
Nov 22, 2010
411
Midland, Georgia
As some of you may know, my pool has been quite problematic with metal staining for many years. For the past 3 years I had been using Metal Magic to control the metal staining but lately, I've been having to use about 2 quarts of Metal Magic a week and have been having problems with chlorine demand, phosphates off the chart (over 4000 ppb) and the water not being as clear as I prefer. I know the consensus here is that phosphates are not a problem with sufficient chlorine but I've decided to do an ascorbic acid treatment followed by replacing as close to 100% of my water as i can to start new. I'm also going to try to not use my SWG and manually dose with liquid chlorine for the rest of this season.

Since I have a vinyl liner, I thought I'd try the tarp method (sump pump in deep end dumping out old water, tarp on pool surface, fill water on top of tarp).

My pool is 16x36 to bottom step (16x39 to top step) so I got the biggest tarp I could find at Harbor Freight (29ftx50ft). It won't be big enough to get to the bottom of my pool but it should get to around 1.5-2 feet from the bottom of the deep end.

In preparation, I removed ladder, hand rail and diving board.

Wish me luck!

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JoyfulNoise

TFP Expert
Platinum Supporter
May 23, 2015
17,216
Tucson, AZ
Best of luck Carlos. Stay safe doing it and don’t be heroic if the tarp gets out of control. Better to let the water mix than fall into a pool with a tarp.

Also, your pool has a ton of spent phosphates in it from the sequestering agents. You are right to be concerned because phosphate levels that high can make the water very reactive to algae growth and, because of your staining issues, you can’t keep the chlorine as high as you’d like.

I’m sure your grass will appreciate all the fertilizer you’re spraying it with 😉
 
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JamesW

TFP Expert
Mar 2, 2011
20,339
That tarp is way too small. You need a tarp that's large enough to fit the entire pool depth.

For example, a 20 x 40 x 8 foot deep pool would need about a 46 x 66 foot tarp.

You put the slack on the pool so that the tarp is never pulling on the edges.

That's going to pull in as soon as you turn the water on.
 

CrystalRiver

Well-known member
Jun 19, 2020
235
Massachusetts
That tarp is way too small. You need a tarp that's large enough to fit the entire pool depth.

For example, a 20 x 40 x 8 foot deep pool would need about a 46 x 66 foot tarp.

You put the slack on the pool so that the tarp is never pulling on the edges.

That's going to pull in as soon as you turn the water on.
It's the biggest tarp they could find. It's better than nothing. It will reduce the mixing of fill and old water, at least at first.
 
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carlos31820

LifeTime Supporter
Nov 22, 2010
411
Midland, Georgia
That tarp is way too small. You need a tarp that's large enough to fit the entire pool depth.

For example, a 20 x 40 x 8 foot deep pool would need about a 46 x 66 foot tarp.

You put the slack on the pool so that the tarp is never pulling on the edges.

That's going to pull in as soon as you turn the water on.
Yes I’m aware that it’s not as large a tarp as I would have liked. It’s the biggest one I could source locally and it wasn’t cheap.

The plan was to minimize the wasting of new water if I let it mix with the old right away as has been the case with multiple drain and refill cycles. As it is, the sump pump isn’t at the very bottom of deep end because the power cord isn’t long enough.

The good news is that the tarp is doing fine after filling for around 6 hours (I turned everything off before going to bed last night). There’s about a foot of water on top of the tarp and nothing is falling in.

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JamesW

TFP Expert
Mar 2, 2011
20,339
Ok. I was thinking that you were going to do a full exchange.

For a full exchange, you need a tarp big enough to go from the deck, down one wall, across the floor, up the other wall and onto the deck.

Basically, the tarp ends up lining the pool like the pool liner, but bigger because it has to go a few feet onto the deck.

You can get a bigger tarp online for a reasonable price.

In any case, thanks for sharing your information with us.

:goodjob:
 

carlos31820

LifeTime Supporter
Nov 22, 2010
411
Midland, Georgia
Tarp water replacement is still progressing as expected. I've added some tarp clips and paracord that will stretch and allow the tarp to slide just past the coping but keep it from falling in the water.

The tarp is already resting on the bottom of the shallow end and is about 65 inches from the deck in the deep end. I estimate it will go about another 2 feet or so before I run out of tarp. I'll cut the water off before going to bed so I can keep an eye on it tomorrow as it continues.

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JoyfulNoise

TFP Expert
Platinum Supporter
May 23, 2015
17,216
Tucson, AZ
I would stop with a foot or two of water in the deep end and then start pulling the tarp back from that end where there is lots of play. Don’t drag the tarp in the shallow end where it is pressed against the liner by water forces.
 

carlos31820

LifeTime Supporter
Nov 22, 2010
411
Midland, Georgia
I would stop with a foot or two of water in the deep end and then start pulling the tarp back from that end where there is lots of play. Don’t drag the tarp in the shallow end where it is pressed against the liner by water forces.
Thanks for the suggestion. I will have to stop with about 1.5-2ft in the deep end because the sump pump power cord did not allow me to have it at the very bottom. The rope holding the sump pump has it suspended against the wall but well off the bottom.
 

carlos31820

LifeTime Supporter
Nov 22, 2010
411
Midland, Georgia
You should get a very good dilution from what you have accomplished with the tarp.
Yes, that was the plan after a serious AA treatment (4.5lbs of AA). Wanted to make sure all staining in plumbing, etc would lift before draining everything.

I guess first order of business will be to test water and add CYA and liquid chlorine. Then work on alkalinity/pH and finally some calcium. I know vinyl pools don't "need" CH but I have a pool heater (mostly bypassed past spring time) so I want to make sure to have some calcium to avoid any issues.
 

JoyfulNoise

TFP Expert
Platinum Supporter
May 23, 2015
17,216
Tucson, AZ
Yes, that was the plan after a serious AA treatment (4.5lbs of AA). Wanted to make sure all staining in plumbing, etc would lift before draining everything.

I guess first order of business will be to test water and add CYA and liquid chlorine. Then work on alkalinity/pH and finally some calcium. I know vinyl pools don't "need" CH but I have a pool heater (mostly bypassed past spring time) so I want to make sure to have some calcium to avoid any issues.
Add liquid chlorine first, no CYA, and wait until you start to see the FC register and hold. The AA and chlorine need to neutralize one another before the FC will start to hold. Then you can get your CYA up to 30ppm. If you see the water go brown/green then you’ve got iron in the water and you should try to filter it out with polyfill in the skimmer.

If no color changes, the. I would then get the FC up to 10ppm and do an OCLT to make sure you don’t have any algae issues. After you pass OCLT, then you can get your CYA and FC up to operating conditions. Don’t worry about pH or TA until you have your FC and CYA where you want them.

A CH of 200ppm is more than enough. No need to go crazy.
 

carlos31820

LifeTime Supporter
Nov 22, 2010
411
Midland, Georgia
Good point about some AA being left and consuming chlorine when I start to re-balance the water. There will be some residual Polyquat-60 since I added around 30 ounces during the AA treatment but it will be heavily diluted.
 

Newdude

Well-known member
Jun 16, 2019
4,437
NY
Bravo Carlos. This is amazing !! I didn't want to jinx you but I foresaw the stairs being the failure point early on. I am very pleased to be wrong.
 
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carlos31820

LifeTime Supporter
Nov 22, 2010
411
Midland, Georgia
Well guys, I have good news and almost bad news. In the interest of transparency for any that come across this post in the future.

As you know, I was thinking that because my sump pump was not at the bottom of the deep end, it would quit sucking water at some point. I did not take into account that the deep-end dive bowl is a smaller area that would drain much faster than when I was draining the entire pool.

So.... I'm working from home and running the sump pump and water hoses as I did yesterday. Around 11am, I went outside to check on things and to my surprise, the sump pump had sucked ALL THE WATER from the pool and had suctioned the tarp tight against the deep end main drain and the sump pump. As I ran to unplug the pump, I saw the tarp being ripped around the sump pump.

Being a tarp first-timer, something I did not think about was that as the pool filled, the tarp would be pushed against the sump pump and it would keep squeezing water out of the deep end. I don't know why I pictured the water getting below the pump and suction stopping as a result. It makes perfect sense, in hindsight, that the tarp would keep pushing water towards the pump.

The good news is that I got all the old water out. The bad news is that I ripped the tarp and initially the tarp had such a strong suction seal against the liner that it was impossible to move it whatsoever. I won't lie, I was freaking out.

What I ended up doing was breaking the suction near the surface wide enough to stick my arm and garden hose down the deep end wall between the tarp and liner. Between the hole in the ripped tarp and the two garden hoses putting water between the tarp and pool wall, the tarp finally broke free of the liner after about 20 minutes of putting additional water behind the tarp. My friend came over and we were able to pull the tarp out from the side (instead of pulling it from the deep end). Close call for sure.

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