WARNING! This procedure is mildly dangerous and potentially very costly if not performed properly, with great care and consideration, and due diligence. WARNING!
WARNING! This procedure involves completely draining an in ground swimming pool, something that is recommended only in a few circumstances. If not performed properly it could, at a minimum, ruin your liner (approx. $2000) and at most require your pool to be rebuilt entirely (approx. $15000). This procedure is only applicable to certain pools based on location. If you have any doubts as to whether to proceed please consult a pool construction professional. WARNING!
NOTE: The instructions and tips herein are written by a novice, not a professional. By reading and using the information in this instructable you agree that you take full responsibility for any damages or injuries caused to your person or property or anybody else's person or property by performing this procedure either properly or improperly and hereby release me from any responsibility for said damages.
I will attempt to make these instructions as general as possible and try to cover as many different scenarios as possible. Bear in mind, however, that they are based on my personal (novice) experience and my observations of the initial installation of my pool's liner by professionals. As such they will lean heavily toward my specific circumstances.
Step 1: Due Diligence
When should a pool be refilled? The answer to this question is most likely, "By you? Never." My research says that the only time a pool should be completely drained is when the liner needs replacing. There may be other circumstances, but I'll leave those for collaborators to fill in. A pool may be partially drained (a third or half way) if the Total Dissolved Solids(TDS) are too high or in a couple of other circumstances which I or a collaborator may fill in later.
I started refilling my pool out of frustration and before I looked into whether or not it's a good idea. That, however, is why I'm writing this instructable: so you won't make the same mistake. As it turns out, given the staining on my liner and the amount of difficulty I had opening the pool this year, my pool's TDS was probably too high so I'm partially vindicated.
What pools should not be refilled? I was relatively sure it was safe to completely refill my pool because I had seen a pro do it a couple of years ago when the liner was replaced. Given that experience and the pool's location on a hill I was reasonable sure that nothing untoward would happen.
The only real indicator I can give you as a novice is what I've read on the topic: once again I'll have to rely on collaborators to fill in the blanks. If your property is close to the level of the water table you should never empty your pool less than a third of the way; maybe not even that if you're very close to the water table or if there have been heavy rains lately.
The only thing keeping your liner attached to the pool wall is that the water pressure on the inside is greater than that on the outside. If you drain your pool and the bottom is below the surface level of the water table then the water from outside with seep in under your liner and it'll appear to float up from the bottom. If your pool's hull - the hard surface installed under the liner (usually plywood, steel, or fiberglass) - is sealed well, as in most fiberglass hulls, the hydrostatic pressure will probably either float it out of the ground as it's emptied or crush it. Also, if water seeps in under the liner as your emptying the pool it may bring in earth with it and cause the hole the pool is in to collapse.
My pool is on top of the highest hill in my area so I was fairly certain nothing would happen. Also, it helped that I had the liner replaced a few years ago and there was no problem with seepage. If you don't know if your pool's bottom is below water level then let a professional do this for you or don't do it at all.
So, should you completely refill your pool? The short answer is no. If you're like me and you've already embarked on the trip and you just want advice then read on. If you're only partially refilling your pool to deal with high TDS then this information will probably be useless to you because you won't be removing but a third or half of the water and the liner should be safe.
Step 2: Intro to Hydrostatic Pressure
Shown in the images is an example of a vinyl lined pool with a hard shell outside and a respectably high ground water level outside the pool. The ground water is just sitting underground saturating the soil but it does in fact have somewhat of a surface to it. As long as the pool water level is equal to or higher than the surface level of the ground water then there is greater pressure from the pool water and thus a net outward force holding the liner against the wall of the pool's outer shell. As water continues to be drained from the pool the surface level of the pool water drops below that of the ground water and a net inward pressure develops. This net inward pressure is a result of the fact that there is more water pressure on the outside than the inside. If the pool's shell is porous or unsealed then water seeps through the shell and collects behind the liner. If this happens quickly then the liner will appear to float up off the bottom of the pool as more water collects below it and more water is removed from above it. If the shell is well sealed and non-porous then the seeping will occur slowly allowing the pool to continue emptying and creating a buildup of pressure on the outside eventually collapsing the walls of the pool's shell or pushing it up out of the ground.
Step 3: When It's SafER to Empty a Pool.
Step 4: Gathering Materials and Tools.
There is very little in the way of materials and tools required to perform this procedure. The following are required, however.
Duck Tape (the name brand, not duct tape)
A water pump ( not your pool's pump )
A contractor or industrial rated wet/dry vac
I recommend you rent the water pump. Your pool pump is designed to function with a certain amount of water in it...the more water you pump out the lower the water level and the more pressure that's put on the pump intake causing the pump to have to work harder - much harder. this will more than likely kill your pump, or at least shorten its lifespan.
When you rent the pump I recommend getting a gas powered one. Compare the capacities of the available models and get the highest capacity one you can afford. At the Ace Hardware where I rented the one I used there was a 52 gallon per minute electric model and a 200 gallon per minute gas-powered model. Doing the math showed that the electric would take about 7 hours to finish whereas the gas-powered model could be done in under 2 hours. I went with the gas model.
Then vacuum will need to run continuously for about 8-12 hours so if you don't have one that can hack that I recommend you upgrade or kiss your shopvac goodbye.
That's it...lets get started with this foolish endeavor.
Step 5: Drain the Pool.
Another thing to consider is that if you live near the water table you must pump the water as far as possible away from the pool even if your pool bottom is above the water table. An entire pools-worth of water being pumped nearby will undoubtedly raise the level of the water table temporarily causing the liner to float which will make it impossible to reset the liner until the water level of the water table returns to normal.
Once you perform your due diligence here it's time to begin. There's no wrong way to do this...I think. You just turn off the pool pump, chuck the suction hose over in the pool, unroll the exhaust hose as far away from the pool as possible, and switch on the water pump.
The pump probably won't be able to get out all the water; I still had about 8 inches left when the pump lost its prime and started sucking air. Use a bucket to bail as much of the remainder as you can and then use the wet/dry vac to remove the rest of the water and any sand and debris. Hold onto the vacuum, though, you'll need it in the next step.
Step 6: Inspect the Liner (optional But Interesting)
One corner had been installed improperly and had pulled away when it was initially filled creating a gap. I pulled the liner up and reinserted it into the rim and pushed pennies into the gap to make sure it stayed. No problems so far. I did notice that the workers who put the liner in must have lost about 5 cents in pennies...I could see the outline in the liner. Note to self...make sure to be present for such things next time you get a new liner.
Step 7: Reset the Liner
To reset the liner do the following:
Pull a small section of the rim of the liner out of the groove that is holding it. Do this about halfway down one of the long sides. Insert a couple of dimes or a nickle into the gap at either end of the section your removing to hold the rest of the liner rim in place. Insert 2-3 feet of the wet/dry vac's hose through the gap and behind the liner. Use the tape to seal the area around the hose so that a vacuum can form. Seal all other gaps if any exist. Run the vac for at least 15 minutes before beginning to fill the pool. If at any time you have to turn off the vacuum then also turn off the water and don't turn the water back on until you turn the vacuum back on and wait 15 minutes. Keep an eye on the liner as the pool fills and work out any wrinkles by pushing them toward the surface before they get too far below the water level.
Step 8: Go Ahead. Refill the Pool.
When the water level is about 3 inches deep in the shallow end of the pool ensure that there are no wrinkles there and then remove the vacuum hose and tape and reinsert the liner into it's groove. Continue filling the pool until it's full.