Pool water chemistry sounds complicated, but it comes down to a handful of numbers. If you keep those numbers in range, your water stays clear, your sanitizer works, your pool equipment lasts longer, and the water is safe to swim in. Let them drift and you end up with cloudy water, algae blooms, skin irritation, corroded pool equipment, and stained pool surfaces.
This guide covers every chemical you need to understand as a pool owner in Tennessee — what each one does, what range to target, and how to adjust it.
The Numbers That Matter
Here is a quick reference for the ideal ranges. We will go through each one in detail below.
- Free chlorine — 2 to 4 ppm
- pH — 7.2 to 7.6
- Total alkalinity — 80 to 120 ppm
- Cyanuric acid (stabilizer / CYA) — 30 to 50 ppm (chlorine pools) or 60 to 80 ppm (saltwater pools)
- Calcium hardness — 200 to 400 ppm
- Total dissolved solids (TDS) — Below 2000 ppm
- Salt level (saltwater pools) — 2700 to 3400 ppm
Free Chlorine: Your Primary Sanitizer
Chlorine is what kills bacteria, viruses, and algae in your swimming pool. When people talk about "pool chlorine" they usually mean free chlorine — the active, available chlorine that is ready to sanitize. This is different from combined chlorine (chloramines), which is chlorine that has already reacted with contaminants and is no longer effective.
The target for free chlorine in a residential pool is 2 to 4 parts per million (ppm). Below 1 ppm and algae and bacteria can start growing. Above 10 ppm and swimmers may experience eye irritation, skin dryness, and bleached swimsuits.
Common chlorine products for residential pools:
- Liquid chlorine (sodium hypochlorite) — 10–12.5% concentration. Fast-acting, no residue, does not add stabilizer. The same active ingredient as bleach, just stronger. Raises pH slightly.
- Granular shock (calcium hypochlorite / cal-hypo) — 65–73% available chlorine. Dissolve in a bucket before adding. Raises calcium hardness and pH. The most common pool shock product.
- Dichlor (sodium dichloro-s-triazinetrione) — Granular, fast-dissolving, contains stabilizer. Good for small adjustments but adds CYA with every dose. Overuse raises cyanuric acid quickly.
- Trichlor tablets (trichloroisocyanuric acid) — Slow-dissolving 3-inch tablets used in floating dispensers, automatic chlorinators, or skimmer baskets. Contains stabilizer. Very acidic — lowers pH over time. The most popular daily chlorination method but contributes to CYA buildup.
- Salt chlorine generator — Converts dissolved pool salt (sodium chloride) into chlorine through electrolysis. Produces chlorine continuously while the pump runs. Requires a salt cell, proper salt levels, and periodic acid washing of the cell to remove calcium deposits.
In Tennessee's summer heat, chlorine gets consumed fast. UV radiation from direct sunlight breaks down free chlorine, bather load introduces sweat, sunscreen, and body oils, and warm water temperatures accelerate chemical reactions. Test chlorine at least twice a week during swim season — more often during heat waves or after pool parties.
pH: The Foundation of Water Balance
pH measures how acidic or basic your pool water is on a scale from 0 to 14. Pure water is 7.0 (neutral). Pool water should be kept between 7.2 and 7.6, with 7.4 being ideal — this matches the pH of human eyes and skin, minimizing irritation.
Why pH matters so much:
- Chlorine effectiveness — At pH 7.2, about 63% of your free chlorine is in its most active form (hypochlorous acid). At pH 8.0, that drops to about 21%. High pH means your chlorine is barely working even when the test reads adequate levels.
- Swimmer comfort — Low pH (below 7.0) causes stinging eyes, itchy skin, and irritated mucous membranes. High pH (above 8.0) also causes eye irritation and dry, flaky skin.
- Equipment and surface protection — Acidic water (low pH) corrodes metal pool equipment — heat exchangers, pump seals, heater internals, stainless steel ladders, and copper piping. It also etches plaster pool finishes and dissolves grout. Basic water (high pH) causes calcium scale deposits on tile, inside pipes, on the salt cell, and on heat exchanger surfaces.
To raise pH, add soda ash (sodium carbonate). To lower pH, add muriatic acid (hydrochloric acid) or dry acid (sodium bisulfate). Make adjustments in small doses, circulate for a few hours, then retest. Overshooting pH in either direction is common when you add too much at once.
Total Alkalinity: The pH Buffer
Total alkalinity (TA) measures the water's ability to resist pH changes. Think of it as a shock absorber for pH — when alkalinity is in range (80–120 ppm), pH stays more stable and does not swing wildly when you add chemicals, when it rains, or when swimmers jump in.
Low alkalinity causes pH to bounce unpredictably, a condition called pH bounce. You add acid, pH drops too far. You add soda ash, pH spikes. It becomes a frustrating cycle. Low alkalinity also makes water corrosive to pool surfaces and equipment.
High alkalinity locks pH on the high side and makes it difficult to bring down. It also promotes calcium scaling on tile, waterline, and inside plumbing.
Raise total alkalinity with sodium bicarbonate (baking soda) — it raises TA without significantly affecting pH. Lower it with muriatic acid — add the acid in one spot with the pump running to lower TA, or broadcast it evenly to lower both TA and pH together.
Always adjust total alkalinity before adjusting pH. Once TA is in range, pH becomes much easier to dial in and hold steady.
Cyanuric Acid: Chlorine's Sunscreen
Cyanuric acid (CYA), also called pool stabilizer or pool conditioner, protects free chlorine from being destroyed by ultraviolet sunlight. Without stabilizer in an outdoor pool, direct Tennessee sun can burn off 90% of your free chlorine in just a couple of hours.
The ideal CYA range for a chlorine pool is 30 to 50 ppm. Saltwater pools can run a bit higher, 60 to 80 ppm, because the salt cell continuously generates fresh chlorine.
The catch: CYA does not break down, evaporate, or get filtered out. It only leaves the pool through splash-out, backwashing, and water replacement. If you use trichlor tablets or dichlor granules as your primary sanitizer, CYA accumulates with every dose. Over months and years, it can climb above 100 ppm or higher.
At high CYA levels, chlorine becomes increasingly ineffective. The stabilizer bonds to chlorine molecules and slows their ability to kill bacteria and algae. A pool with 150 ppm CYA and 3 ppm free chlorine has far less active sanitizer than a pool with 40 ppm CYA and 3 ppm free chlorine.
The only practical way to lower cyanuric acid is to drain a portion of the pool water and refill with fresh water. There is no chemical you can add to reduce it. If your CYA is at 100 ppm and you drain half the pool and refill, you will be at roughly 50 ppm.
Calcium Hardness: Protecting Pool Surfaces
Calcium hardness measures the dissolved calcium in your pool water. The ideal range is 200 to 400 ppm for plaster, gunite, and concrete pools. Vinyl liner pools and fiberglass pools are more forgiving and can run lower (150–250 ppm) since they do not rely on calcium in the water to protect the surface.
Low calcium hardness makes water aggressive — it will pull calcium from wherever it can find it, which means your plaster, grout, tile, and concrete deck. Over time this causes pitting, etching, and rough pool surfaces that are more prone to algae attachment.
High calcium hardness leads to scale deposits — white crusty buildup on the waterline tile, inside pipes, on the heat exchanger, and on the salt cell. Scale restricts water flow, reduces heater efficiency, and damages equipment.
Raise calcium hardness with calcium chloride. Lowering it requires partial drain and refill with softer water, similar to fixing high CYA. Tennessee tap water varies by municipality — some areas around Dickson County have moderately hard fill water, which means calcium hardness can creep up over time as water evaporates and is replaced.
Phosphates and Nitrates: Algae Food
Phosphates and nitrates are nutrients that feed algae growth. They enter the pool from fertilizer runoff, decaying leaves and organic debris, bird droppings, soil, sweat, and some municipal water supplies. Phosphates do not directly harm swimmers, but high levels give algae an easy food source.
Keeping phosphates below 300 ppb (parts per billion) removes a key ingredient algae needs to bloom. Phosphate removers (lanthanum-based products) bind to phosphates and let the filter remove them. They are not a substitute for proper chlorination, but they reduce the conditions that favor algae growth.
In Dickson County, where many pools are surrounded by mature trees, grass, and landscaping, phosphates can be a persistent problem — especially after heavy rain washes lawn fertilizer and mulch runoff into the pool.
Total Dissolved Solids and When to Drain
Total dissolved solids (TDS) is the sum of everything dissolved in your water — salt, minerals, chemical byproducts, organic compounds. Over time, as water evaporates and you add chemicals and fresh water, TDS climbs. Above roughly 2000 ppm (or 5000–6000 ppm for saltwater pools, since salt itself counts toward TDS), water becomes harder to balance, chlorine becomes less effective, and the water can taste or feel off.
High TDS is another reason for periodic partial drain and refill. Most residential pools benefit from replacing 1/3 to 1/2 of their water every 3 to 5 years, or sooner if TDS, CYA, or calcium hardness are stubbornly out of range.
How to Test Your Pool Water
You cannot manage what you do not measure. There are several ways to test pool water chemistry:
- Test strips — Dip a strip in the water, wait 15–30 seconds, and compare the color pads to the chart on the bottle. Fast and cheap, but less accurate than liquid tests. Good for a quick check between thorough tests.
- Liquid test kits (DPD / OTO) — Add reagent drops to a water sample and compare colors. More accurate than strips. FAS-DPD drop-count kits are the gold standard for measuring free chlorine precisely — you count drops until the color changes, giving you an exact reading instead of estimating between color shades.
- Digital testers — Electronic photometers and colorimeters give numeric readings. Expensive but very precise. Worth it if you are managing chemistry closely on a saltwater pool or commercial pool.
- Pool store testing — Many pool supply stores offer free water testing with a computer-generated report. Bring a water sample collected elbow-deep away from return jets. Good for a detailed baseline but not practical for the twice-weekly checks you need during summer.
For most homeowners, a combination of weekly test strips for quick monitoring and a liquid test kit (Taylor K-2006 or similar FAS-DPD kit) for thorough checks every week or two is the best approach. Always test in the shade — sunlight can affect reagent accuracy.
The Order of Operations for Balancing
When multiple readings are off, adjust them in this order:
- 1. Total alkalinity — Get this in range first (80–120 ppm). It stabilizes everything else.
- 2. pH — Once TA is set, adjust pH to 7.2–7.6. It should hold better now.
- 3. Calcium hardness — Adjust to 200–400 ppm. This changes slowly and usually only needs attention seasonally.
- 4. Cyanuric acid — Check CYA and adjust to 30–50 ppm. Drain if too high. Add stabilizer granules if too low.
- 5. Free chlorine — Now that everything else is in range, set your chlorine level. It will work efficiently and hold better with balanced water.
Make one adjustment at a time, circulate for at least 4–6 hours (ideally a full turnover), then retest before making the next change. Dumping multiple chemicals in at once is how people end up with wild swings and overcorrections.
Common Mistakes New Pool Owners Make
- Only testing when the water looks bad — By the time water looks cloudy or green, chemistry has been off for days. Test on a schedule regardless of appearance.
- Adding chemicals without testing first — "Just throw in some chlorine" leads to overshoot, wasted chemicals, and sometimes makes the problem worse.
- Ignoring cyanuric acid buildup — Trichlor tabs are convenient, but CYA accumulates silently. By mid-summer you might have 120+ ppm and wonder why your chlorine is not working.
- Not running the pump long enough — Chemicals only work in moving water. Your entire pool volume should circulate through the filter at least once per day. For a 20,000 gallon pool with a pump rated at 40 GPM, that is about 8 hours of run time minimum.
- Shocking during the day — Unstabilized shock (cal-hypo, liquid chlorine) gets destroyed by UV sunlight within hours. Always shock at dusk or after dark for maximum effectiveness.
- Adding chemicals through the skimmer — Trichlor tabs in the skimmer create a slug of highly acidic, high-chlorine water that flows directly through your pump, filter, and heater — corroding seals, gaskets, and heat exchangers. Use a floating chlorinator or inline chemical feeder instead.
- Neglecting the filter — A dirty filter means poor circulation, poor water clarity, and chemicals that cannot do their job. Stick to a regular backwash and cleaning schedule for your sand filter, DE filter, or cartridge filter.
Tennessee-Specific Considerations
Pool chemistry in Middle Tennessee has some local quirks worth knowing:
- Hard fill water — Many areas around Dickson, Charlotte, White Bluff, and Burns have moderately hard municipal or well water. When you fill or top off your pool, you are adding calcium and minerals each time. Monitor calcium hardness more closely if you top off frequently in summer.
- Pollen season — Spring pollen from oak, pine, and hickory trees is intense in Dickson County. Pollen itself does not harm chemistry directly, but it creates a surface film that clogs skimmer baskets, reduces surface tension, and adds organic load that consumes chlorine faster.
- Afternoon thunderstorms — Summer storms in Tennessee are frequent and heavy. Each storm dilutes sanitizer, washes in contaminants, and can shift pH and alkalinity overnight. Test and adjust after every significant rain event.
- High summer humidity — Humid air slows evaporation slightly compared to arid climates, but water temperature stays high — 85°F or more in July and August. Warm water accelerates chlorine consumption and algae growth. You will use more chemicals in a Tennessee July than you would in May.
- Red clay soil — If your pool is near exposed earth or a construction area, iron-rich Tennessee red clay can stain pool plaster and turn water a rusty brown. A metal sequestrant helps bind dissolved iron so the filter can remove it.
When Chemistry Gets Overwhelming
Balancing pool water is manageable once you build a routine, but it does take consistent attention — especially during Tennessee's long, hot swim season. If you would rather spend your weekends in the pool instead of testing it, that is what we are here for.
At Dickson Pool Cleaning Service, we test and adjust your water chemistry on every single visit. We serve Dickson, Charlotte, White Bluff, Burns, Vanleer, Slayden, and everywhere in between. Weekly and biweekly plans start at $65 per visit — see our plans page for the full breakdown, or give us a call.