This was well said in another area of the site, but I thought it bared repeating here.
CarlD said:It's actually all simpler than most people think. There's no magic, no secret formula.
Basically, you worry about Chlorine and pH--and everything else is ancillary to that.
Chlorine is controlled with bleach. Levels can safely be much higher than pool stores and pool books tell you. You can use nothing but bleach as your chlorine forever.
pH is raised with ordinary 20 Mule Team Borax, lowered with ordinary Muriatic Acid (available at hardware stores and Home Depot/Lowes).
Total Alkalinity is merely (mainly) a buffer to keep pH stable--raise T/A with Arm&Hammer baking soda. Lower it--well that's trickier.
CYA/Stabilizer keeps chlorine from breaking down too fast. But it's a 2-edged sword and the CYA level affects the ideal chlorine level. Easy to add, tough to lower.
Calcium is needed for concrete pools, irrelevant for vinyl pools.
Most other chemicals are useless junk. The ones that aren't junk are ONLY useful if something's messed up.
"Shock" is a verb, not a noun. You don't buy "Shock". You "Shock" your pool by raising the chlorine level high enough to kill everything growing in it.
And you can't do anything right without a proper test kit.
That's it in what? Nine lines.