My post yesterday on sand filters generated some questions, better answered here than in the comments. So, let's see if I can address them. I'm no expert, and Google is your friend, I'm sure that better answers can be found online, but I'll give them a shot based on my experience.
Milady and I installed the pool in April/May 2007. The sand in the filter is seven years old. We noticed earlier this year that the filter wasn't catching as much of the normal crud that moves through the system as it should, so we started casting about for answers. Obviously, the filter wasn't doing as good a job as it should and in our research we learned that locally, people tend to change the sand in their filters every three to five years.
It's a Triton II, a fairly standard design, and easy to access. So, to the questions.
Mostly Cajun asks if sand wears out> When I opened the top of the filter, I could see that the sand was dirty, and the sand didn't feel like good river sand. It was less abrasive, didn't have those nice sharp edges we associate with sand, and it just felt different, and it looked dirty. Of course, it has been filtering water for seven years, so I expected it to be dirty. I back-wash it regularly when I sense a reduced flow, but the filter didn't seem to be catching as much dirt, so we decided to change the sand. My particular filter takes 300 pounds, and a local lumber yard was running a sale on pool filter sand, so I picked up six bags on sale. It took me about an hour to scoop out the old sand and pour in the new sand. Not a bad job, but a dirty one.
Rivrdog asks if that filter could be used for primary filtration of creek water? I don't know why not. We don't cover our pool during the winter months, and when I start cleaning the pool in the springtime, it's pretty cruddy. The filter cleans the water quickly, although before drinking, you'd need to sanitize it and have it tested, but it would be clean water.
We use a salt system, which uses a charged grid to release the chlorine in the salt to sanitize the pool. It needs to be cleaned regularly, normally twice per year, a process that takes about 30 minutes and is fairly straightforward. The salt system has up-sides and down-sides, but the biggest upside is that it uses salt rather than toxic chlorine to sanitize the pool. The salinity of the pool water is about the same as human tears, so the grandkids don't come out of the pool with red eyes. And pool salt is cheap as regular salt, because it is simply salt. I have used livestock feed salt on the occasion that I could't find pool salt. Morton salt is Morton salt, and I could probably use table salt. The pool normally uses six or seven, 50 lb bags of salt per year. Total chemical expenditures on my pool normally runs about $50.00 per year. Salt is cheap and it's the only chemical I put in it.
That's not exactly true. In the winter months, when the water temperature gets below 50F, the system quiits making chlorine, so we have to supplement a little bit. Milady normally picks up a little bucket of chlorine tablets and we'll drop one in the skimmer during the winter months. So, add another $30-$40 for the chlorine tablets. Those little buckets, when empty, make a great container for storing range brass and cast bullets.
I hope this answers your questions.