This instructable is based on my experience refilling my in ground swimming pool. I learned a few things doing so and wanted to pass those along.
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
Before you begin there are some things that must be considered. When should you drain and refill your pool? What makes one pool safer to drain than another. What circumstances should cause you to rule refilling out entirely? There are many more questions that should probably be asked but I don't have the experience to know what they are right now. As I research more into this topic I may update this instructable to include new information. These questions can be answered right now thought with a little research.
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.