Guide
How to Balance Pool Water — FC, pH, TA, CH, CYA
A practical order for balancing pool water: free chlorine, pH, alkalinity, calcium, and stabilizer — what to fix first and why.
Balancing pool water means getting the big five into a working range: FC, pH, TA, CH, and CYA (plus salt if you have a saltwater chlorine generator). Order matters. Fixing pH before you have sanitizer is how you polish a dirty glass.
Suggested order
- Sanitizer (FC) — water should be disinfected while you tune the rest. Clear algae first if the pool is green (SLAM).
- CYA — stabilizer sets how much FC you need. Don’t chase a “perfect 3 ppm” if CYA is 80.
- TA (total alkalinity) — the buffer that keeps pH from yo-yoing.
- pH — comfort, chlorine efficiency, and surface protection.
- CH (calcium hardness) — plaster and scale risk; change slowly.
CSI (Calcite Saturation Index) is the combined scorecard once the pieces are in play — useful, not a substitute for clean water.
Targets (residential, trouble-free style)
Exact bands depend on surface type and CYA. Rough mental model:
- FC: high enough for your CYA (and weather); don’t run on empty overnight.
- pH: roughly mid-7s for most pools.
- TA: often mid-range so pH isn’t twitchy.
- CH: higher for plaster; lower can be OK for vinyl — know your surface.
- CYA: enough for sun protection; not so high that FC targets become absurd.
What to adjust with
- Raise FC → chlorine products (see chlorine calculator).
- Lower pH / TA → muriatic acid or dry acid (dose carefully; retest).
- Raise TA → baking soda.
- Raise pH (when TA is OK) → soda ash (sparingly).
- Raise CH → calcium chloride.
- Raise CYA → cyanuric acid (slow dissolve; patience).
Common mistakes
- Testing once a month in peak season — see how often to test.
- Chasing pH daily while TA is wrong.
- Ignoring CYA when FC “won’t hold.”
- Dumping full acid demand at once — prefer thirds and retests.
Make the loop boring
Balance isn’t a weekend project every time. It’s a short weekly habit: test → adjust → log. Pooldex turns the adjust step into exact amounts for the chemicals you stock, with safety-first acid guidance.