safe depth to drain vinyl pool w/vinyl stairs

[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-

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.

PoolDoc

Ben, 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-

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!