safe depth to drain vinyl pool w/vinyl stairs

[ScottsdaleSwim]

I'm getting ready to drain my inground vinyl lined pool at least halfway. My husband is freaking out that we shouldn't drain it. One place on the steps has pulled away slightly (actually our realtor did it when we were looking at the house, she had never seen a vinyl liner and wanted to see what was behind it) and continues to pull away even after we shove it back in there. But it's minor.
http://img106.imageshack.us/img106/3065/aaaaaaaaaapool8nv.th.jpg So here's my question. I know it's safe to drain it at least half way...but even with vinyl stairs?
He's got me totally paranoid that our pool will sink through the ground and suck us down with it!

I hate the coping btw, how hard it is to change that? Curious..

Thanks.

Oh, I'm draining because my cya is over 110 now.

[cheshamjim]

First, I'm new to this board and to PoolSolutions, so keep that in mind when reading this post. I'm answering because I have recent experience with partially draining my pool earlier this Spring. I know others will be along to give you the best advise.

Be veerrrry careful!!!. For reasons that are beside the point here, I drained my pool down about 18" from the normal water line (just under 6,000 gallons). When the vinyl liner began to billow inward significantly, I stopped immediately. Luckily, I didn't do any real damage and when I refilled the liner pretty much went back to its original position (except for a couple of minor wrinkles on the bottom).

I believe that ground water can cause real problems when draining a vinyl pool. I've even heard of vinyl liners floating right up out of their reinforcing walls.:eek: This is not good. Maybe ground water is not an issue in Scottsdale.:confused:

I too have CYA above 100. I'm simply maintaining a high chlorine content as recommended by Ben's Best Guess CYA chart http://www.poolforum.com/pf2/showthread.php?t=365. (http://www.poolforum.com/pf2/showthread.php?t=365)I'm going to live with my high CYA for the rest of this season, then when I reopen next Spring I'll see where my CYA stands. If its still unacceptably high, I'll drain some, but not all of my pool water.

I'll be following this thread with interest since you and I have the same reasons for wanting to drain our pools.

-Jim

[Phillbo]

there was a method posted here a while ago where you lay in a plastic sheet on the water. you then pump the water out from under the plastic and add water to the top.. basically you can pump out the bad water without a lot of mixing from the good.

[cheshamjim]

I remember that thread and was part of it. I think it was Watermom who suggested an oversize tarp could be laid across the pool and new water added to it. As the rate of incoming new water and outgoing old water are kept approximately the same, the tarp would form a membrane against the sides and bottom of the existing liner due to the weight of new water.

This really sounds like a good idea to me, but when I posted a new thread asking about the experiences of anyone who might have had success with this approach, I got no response -- either positive or negative.

I will probably be trying it next spring if my CYA doesn't come down over the winter (and from what I read in these forums, it most probably won't).

-Jim

[Watermom]

Actually, it was Al (Poconos) who suggested this method. Don't know if he actually has done it himself or not. Maybe he'll comment on it for you.

[ScottsdaleSwim]

I didn't drain this weekend hoping for more responses.

The tarp would have to be the size of the liner. It can't just be the length and width of the pool because you have to account for the depth...or at least half of the depth depending on the amount you needed to drain - and then some so that you can hold it down on the perimeter of the deck, otherwise it would slide into the pool.
I'm not sure I could find a tarp that large.

[Phillbo]

I don't think the barrier has to extend out of the pool, only form a layer bewteen the out flow and in flow .. keeping the 2 at the same flow rate is tricky I bet. most pumps move a LOT more water than the hose can put back in .


Why not just enjoy the pool for the rest of the summer and then drain it while it's not being used ?

what part of Scottsdale?

[ScottsdaleSwim]

Because you can't completely drain a vinyl pool. It can ruin the liner, float the whole pool or worse. I've heard mostly horror stories about draining a vinyl pool.

How would you keep the tarp on top of the existing pool water and keep the water dispersed evenly enough so that the tarp doesn't slip into the water and mix the new water with the existing water if you don't have it secured around the pool?

That would be like floating saran wrap (unsecured) on top of a bowl- half filled with water and not expecting it to slide under.

I'm having a hard time explaining it...does that make sense?

[tenax]

4 winters now, i have drained my water down about 22 inches from the top edge (which puts it about 2 inches below my jets) vinyl pool vinyl stairs.no problems whatsoever and the pool store's recommendation..

from the standpoint of how much water would be then left in my 15,000 gallon pool? well, at the shallow end, about 26 inches.i have to figure i've drained at about 40% if it to get below the jets. and yes, we do get winter here in my part of alberta canada. (about 45 minutes north of the montana border)

[cheshamjim]

Scotsdale, you are absolutely correct about needing a tarp large enough to not only accomodate your pool's length and width, but the depth as well. We are unlikely to find a tarp that big at the local Lowe's or Home Depot.

I think the word "tarp" might be a little misleading for our purposes. I think plastic sheeting better describes what we are talking about to accomplish this job. I Googled the term and found this (http://www.usplastic.com/catalog/product.asp?catalog%5Fname=USPlastic&category%5Fname=66&product%5Fid=1413#). This is expensive material in the sizes we need ($130 for a 32' x 100' roll), but I think I'll go for it next spring.

The way I visualize this working is this. My pool is 16' wide x 32' long x 6' at the deepest location (we don't dive :)). I figure the 32' wide roll would be adequate for me cut to a length of 44' (the roll is 100' long).

I'll spread the plastic film over the pool and maybe temporarily put weights on the corners to keep the breezes from blowing the sheet off. Then I'll add water on top of the sheet which will keep the new water separated from the old. I'll add enough new water starting out to get the sheeting to sink down and against the old water and the exposed pool walls. Then I'll start pumping the old water out. Most sump pumps will pump water faster than new water can be added, so I'll pump and stop, fill and stop, pump and stop, etc...pumping and filling need not be done simultaneously and in perfect synchronization.

The sheeting I have referenced is only 4 mils thick (.004") but the sheet really shouldn't be stressed since it will essentially be in equilibrium. I think it will work fine.

While I've never done this, I'm confident that by draining slowly and observing whether, in fact, the sheet is being forced effectively against the pool walls, I can control things. If things start to go south, I can abort the process. I'd be out the cost of the sheet and the rental for a submersible sump pump :(, but I think its worth the risk to get my CYA right.

I sure would be thankful if anyone who sees some problem with this plan would speak up.

-Jim

[cheshamjim]

Actually a complete drain using a plastic sheet to form a membrane between the old and the new water is not diluting water. It is replacing it. Your suggested method is diluting it. I don't know if this is an important distinction

It had occured to me to drain a little at a time, gradually diluting the CYA content, but total draining seems so much more direct.

Which is most efficient, less trouble, less money, and less time? Would the dilution method require more water or less to get the desired results (water is really, really expensive where I live)? The answers may be obvious to some, but not to me. Maybe I'll crunch a few numbers and try to figure that last question out.

-Jim

[cheshamjim]

I graduated from U of HK, but I did the math anyway. In my pool, I figured it would take 6 drains of ≈25% each to go from ≈125 ppm CYA to ≈20 ppm. That's a little over 23,000 gallons in my 15,400 gallon pool.

I am not a math wiz and these results may be "all wet." Nevertheless, I think I'll stick to the total drain using plastic sheeting.

-Jim

[ScottsdaleSwim]

Each time you drain and refill it is less and less effective.

Take a glass filled with grape juice, drain half and fill with water. See how diluted it is?
Now take another glass filled with grape juice, drain 10%, refill. Repeat this and see how long it takes to get to the same dilution as the first glass.

Then you can actually see what PoolDoc is talking about instead of doing the math. That's how I explained it to my husband.

I didn't go to college so I guess I was lucky to be able to figure it out ;)
Common sense really.

I drained halfway today and the pool is fine. My liner is only one year old and was pulling away near the steps a little already. I secured it the best I could in the track and as the water gets near the step I'll vacuum the air from behind the liner. I'm actually glad it was loose. I noticed the metal plating had come loose (it was just taped to the other metal) so I was able to repair that.

I only needed to do a partial drain so I felt I was pretty safe. I'm in Scottsdale Arizona and the water table isn't even close to being a problem. Had I been doing a full drain, I would be in search of a very large tarp. Hopefully I won't ever have to do that.

Thanks for all the input. This website and the contributers are priceless.

[cheshamjim]

why is it really necessary to tell the old water from the new water? The way you do it is just drain a foot then refill a foot repeatedly. Both ways you are diluting the pool water.Yeh ... and this kinda seemed like common sense when I read it. Besides, I didn't want to run out and get some grape juice.:) But I do see your point and its a darned good analogy.

-Jim

P.S. - I didn't really go to college either. U of HK is "The University of Hard Knocks." Now ain't that clever?

[ScottsdaleSwim]

Very clever-:p

Pool looks great btw! I even replaced the manifold because I was getting DE in the pool. It came with a new ....oh what is that thing called...the screen on the top...bleeder tube and sock.

A couple of stubborn wrinkles on the top step but they were there when we moved in. I'll wait until the water is really warm (hot!) next week when we hit 109 and then work on those.

[cheshamjim]

If you know what you are doing, and can apply an adequate vacuum behind the liner, it's usually possible to drain further. But if the liner is old, or was badly installed, even that was risky.

The vinyl sheet method is MUCH safer in this situation.

PoolDocBen, is this an endorsement of the vinyl sheet method as posted here?

And I am interpreting your suggestion about applying a vacuum behind the liner (if I knew what I was doing, and I don't, so I won't) would be to evacuate water, not air.

A clarification would be really helpful.

-Jim

[cheshamjim]

Very clever-:p

Pool looks great btw! I even replaced the manifold because I was getting DE in the pool. It came with a new ....oh what is that thing called...the screen on the top...bleeder tube and sock.

A couple of stubborn wrinkles on the top step but they were there when we moved in. I'll wait until the water is really warm (hot!) next week when we hit 109 and then work on those.So, you never had to use the ol' tarp method eh?

I'm glad to hear about your good results. I was just hoping someone would try this plastic sheet business before I try it next spring.

I had a pool contractor over yesterday to give me a quote for a filtration conversion to a sand filter. I mentioned the plastic sheet draining technique to him and he sure laughed a lot.

EDIT: What is your CYA reading now?

-Jim

[ScottsdaleSwim]

My Cya is about 45..which is still a little high but hey, it's SO much better than it was.

I didn't have to use the tarp method but I have a few little wrinkles in the top step. Did I say that already? They were there before and honestly, it was hotter than heck and there was no way I was going to stand in the sun and smoosh them around. The water is HOT. It's just HOT here. 113 today.
Where was I?

Oh, yes- the pool looks fabulous. The alkalinity level was about 140 so I added acid and I'm aerating through the night. That should help with the temperature also.

Your contractor laughed but had no other solution? He'll probably suggest it to another client and act like it was his idea!