Pool School — Water, Settled
Straight answers, less is more, no upsell. The water's simpler than they told you.
Most pool problems come from doing too much, not too little. A balanced pool needs a handful of numbers in range and enough chlorine to do its job — not a shopping cart of bottles. Less is more; more chemicals usually means more problems. Here's everything you need, in plain English, whether it's your first summer or your tenth.
Photo: Chris Grazioli, CC BY 2.0Above-ground poolsGot an above-ground pool?Every guide that applies to an above-ground pool, organised the same way as this page — plus the ones only an above-ground pool needs: salt on a steel wall, a pump that won't move water, the cover and the pillow.Go to Above-Ground Pool School Calculate
Exact doses and targets — no guessing, no overshooting.
Chemical dosing calculatorHow much of what to move any level — chlorine, pH, alkalinity, calcium, stabilizer, salt.Free · on-device📈 Pool TrackerLog every test, get each number judged against your pool's target + the exact dose, and watch the trends. Free, on-device, no account.Water balance calculator (LSI/CSI)Corrosive, balanced, or scaling? The one index that ties your five numbers together.Pool volume calculatorHow many gallons is your pool? Every dose starts here.Salt vs. chlorine cost calculatorIs a salt system actually cheaper for your pool?
Learn the basics
Start here if you're new. The whole of pool care in a few short reads.
Less Is More: The Whole of Pool Care in One IdeaStart here. The one idea that makes every other pool problem simple — and cheaper.How to Test Your Pool Water (and Why Strips Lie to You)Strips and store tests hide the two numbers that matter most. Here's how to read your water for real — and the one kit to own.The 5 Numbers That Matter (and Their Target Ranges)Target ranges for every level, plus the FC/CYA chart — the single most important table in pool care.How Chlorine and CYA Actually Work (the Science Behind the FC/CYA Chart)Why free chlorine has to rise with CYA — the hypochlorous-acid science behind the FC/CYA chart, plainly.Do I Still Have to Test a Salt Water Pool?A salt system makes chlorine, not decisions. Here's what you still test — and the two numbers salt quietly pushes out of range.
Myths, settled
The pool-store gospel, fact-checked. A little reality, so you stop buying bottles you don't need.
Myth, settledDo You Have to Shock Your Pool Every Week?No. 'Shock' is a chlorine level you reach for a problem — not a weekly product or ritual.Myth, settledAre Salt Water Pools Chlorine-Free?No. A salt pool IS a chlorine pool — the cell just makes the chlorine for you, from salt.Myth, settledDo You Need Phosphate Remover?For almost every pool, no. Enough chlorine kills algae no matter how many phosphates feed it.Myth, settledDo You Need Algaecide?No. Proper chlorine prevents algae. Skip routine algaecide — and avoid the copper ones entirely.Myth, settledDo You Have to Run Your Pool Pump 24/7?No. A few hours to skim and mix your chemicals is plenty — chemistry sanitizes the pool, not laps through the filter.Myth, settledIs a Copper or Mineral Pool Chlorine-Free? (Is Copper Safe in a Pool?)Copper kills algae, but it's not a sanitizer, it stains, and it never leaves. A 'mineral pool' just runs less chlorine — not none.Myth, settledCan You Use Bleach in a Pool Instead of Chlorine?Bleach is the exact same chemical as pool 'liquid chlorine,' just weaker. It works fine. The only catches are strength and cost — use plain unscented, and buy fresh.Myth, settledIs Pool-Store 'Alkalinity Up' Just Baking Soda? (Pool & Hot Tub)It's the identical chemical — sodium bicarbonate — at several times the price. Baking soda raises alkalinity, not pH. What it does, how much, and the hot-tub version.Myth, settledCan You Lower Alkalinity Without Lowering pH? The 'Acid Slug' MythAcid lowers pH AND total alkalinity — always, together. The 'slug' or 'acid column' trick doesn't spare your pH; it just risks etching your plaster. The real fix is acid, then aeration.
Fix a problem
Jump straight to what you're dealing with. Answer first, the why underneath.
Start here🩺 Diagnose My PoolPick your symptom, enter a couple of numbers, get the diagnosis + exact target + fix. The fast way in.My Pool Is Green — How to Clear It (the SLAM Method)Green, cloudy, or hazy water; algae on the walls or floor.Green but My Chemical Levels Look Fine?Algae or cloudiness, but your test (or the pool store) says chlorine is fine.Mustard Algae That Comes Back (When Levels Are Good)Yellow/mustard (or green-yellow) dust on shaded walls and floor that brushes away and returns.Are Pool Stores a Scam? The Honest AnswerYou leave the pool store with a cart of chemicals and a printout — every time.Strong Chlorine Smell and Burning Eyes? You Need More Chlorine, Not LessA strong 'chlorine' smell and red, itchy, burning eyes after swimming.My Pool Is Cloudy but Not Green — What's Going On?Milky, hazy, or dull water — but it's not green and you don't see algae.CYA Too High? Why Your Chlorine Quit (and How to Actually Lower It)Your chlorine 'reads fine' but does nothing — or the pool store told you the pool has 'chlorine lock.'How to Recover Your Pool After Wildfire Ash, Smoke, or a StormWildfire ash, heavy smoke, or storm debris just fouled your pool — gray or cloudy water, a chlorine that won't hold, and gunk settling on the bottom.Pool Stains, Scale & Scum: What Each Mark Is and How to Remove ItA brown stain, a white crust, a greasy waterline ring — four different marks, four different fixes. How to tell them apart, remove each (the cheap way), and keep them gone.Black Algae in a Pool: Why It Keeps Coming Back (and How to Actually Kill It)Dark black or blue-green spots that come back after brushing and shrug off shockIn-Ground Pool Losing Water: Find the Leak Before You Buy AnythingYou're topping the pool up more than once a week, the water bill jumped, or the level is visibly below the skimmer mouth.Green Hair and Straw Hair After Swimming: It Isn't the ChlorineHair turning green after swimming, or going dry, dull and straw-like through the season.
Seasonal & away
Closing, opening, and leaving town — the calendar jobs, done in order.
How to Open an In-Ground Pool in Spring (Without Buying a Start-Up Kit)Open early, chlorinate immediately, test before you buy anything. The in-ground opening sequence, plus the ammonia check that stops a spring disaster.How to Prep Your Pool Before Vacation (So You Don't Come Home to Green)The leave-it-safe checklist — build a chlorine reserve, raise FC before you go, run the pump, cut the sun. Come home to clear water, not green.How to Close an In-Ground Pool for Winter (Hard-Freeze Close vs. Florida "Winter Mode")Freeze country closes the pool. Florida doesn't. Both in-ground procedures step by step, including the freeze-night plan for warm climates.Mesh vs. Solid Pool Cover: The Trade-Off You Were Taught Is a Budget-Tier ProblemMesh drains, solid blocks light — except the premium covers on both sides now do both. What the choice actually turns on, and why a 'solid' cover usually isn't.How to Store Pool Floats for Winter (What the Makers Actually Say)Clean, dry, check, roll, store dark. What Intex, SwimWays, Big Joe and FUNBOY actually tell you, the bleach and cold-garage arguments settled, and a Florida version.Year-Round Pool Chlorination in Florida (You Don't Close, You Shift)A Florida pool runs year-round — you dial chlorine demand up in summer and down in winter, you never truly close. The season-by-season plan for CYA, free chlorine, the salt cell, and pump hours.
Look it up
The charts, definitions, and how-it-works guides — grouped by topic, for when you just need the number.
Water chemistry
Pool pH: Why It Rises, and How to Actually Control ItPool pH almost always drifts up — that's normal outgassing, not a mistake. Here's why, what raises and lowers it (and what each does to alkalinity), the targets, and why LSI is the real boss.Water Balance: Is Your Pool Corrosive or Scaling? (LSI/CSI, Plainly)Your numbers can each be 'in range' and the water still corrode or scale. The one index that ties them together — plainly, no products.Borates in a Pool: What They Actually Do (and What They Don't)The closest thing to an easy button in pool chemistry — and it still isn't one. Borates hold pH steadier, keep scale off a salt cell, and stay put until water leaves the pool. What they do, what they don't (two claims we had wrong, corrected), and which of the two dosing routes is actually cheaper.When Is It Safe to Swim After Adding Chemicals?Wait times for chlorine, acid, shock, CYA and more — and the one test that actually decides it.How to Remove Metal Stains with Ascorbic Acid (the Full Procedure)Ascorbic acid lifts iron stains fast — but it moves the metal into the water, it doesn't remove it. The full ordered procedure + the sequester-or-it-comes-back catch.How Fountains, Bubblers & Spillovers Change Your WaterFountains, bubblers, and spillovers all aerate the water — which raises pH, uses a bit more chlorine, and cools the pool. Here's how to work with it.
Chlorine & salt
Salt vs. Chlorine Pool: What Converting Costs, and What Salt Does to Your EquipmentThe same sanitizer arriving a different way — so judge it on equipment, not water. The conversion cost, the cell that decides the math, and the four things around your pool that salt reaches.Salt Water Pool Chemistry: Why the pH Climbs, and What to Set the Cell AtWhy a salt pool's pH rises, why alkalinity is the lever and the cell setting isn't, and the targets that actually differ from a chlorine pool.Which Chlorine Should You Use? Ranked by What Else It Puts in Your WaterLiquid, tablets, cal-hypo, dichlor, salt — same sanitizer, different baggage. Ranked by what else each one adds to your water (and when to break the rule).Chlorine Alternatives for Pools: What Actually Replaces It (Salt, Ozone, UV, Ionizers, Bromine)Salt is chlorine. Ozone, UV, and mineral systems only reduce it — they carry no residual, so you still chlorinate. One system is truly chlorine-free (biguanide), and it's a downgrade for almost everyone.How Long Does a Salt Cell Last? (And How to Make Yours Last Longer)Rated in hours, not years — usually 3–7. Why the cell wears out, the real ways to make it last longer (oversize it, don't over-clean it), and how to tell when it's done.Why a Salt Pool Scales Faster — and How to Fix Calcium BuildupThe white crust on your salt cell and tile isn't the salt's fault — it's calcium and pH. Why a salt pool scales faster, and the step-by-step fix (no anti-scale bottle required).
Equipment & filtration
Single-Speed vs. Variable-Speed Pool Pump: What the Rules Say and What It SavesVariable speed, and on a big pump it is the only new option — Florida field metering puts the saving at 68%. What the federal rules actually require, with measured watts for 10 pumps.How Long Should You Run Your Pool Pump — and at What Speed?Two pools, two answers. If you add chlorine yourself the pump is a skimmer and a mixer; if you run a salt cell it is a chlorine machine and the sun sets the hours. Plus the rule nobody publishes: your minimum RPM is set by your equipment, not your pool.Sand & Cartridge Filter Maintenance: When to Clean, and When Not ToWrite down your clean pressure the day you service the filter — that single number is what makes every other rule here work. Then clean on pressure, not on the calendar, and understand why a slightly dirty sand filter filters better than a spotless one.Your Pool Filter Is a Pressure Vessel (And It Can Take the Lid Off)Filters run under real pressure and trapped air can launch the lid. The manufacturer's own procedure, and what to check before you open yours.Sand vs. Cartridge vs. DE: Which Pool Filter Should You Buy?Cartridge for simple and small, sand for set-and-forget, DE for the clearest water if you accept the labour. Plus the finding no rival publishes: the micron numbers everyone quotes aren't maker specs.Sand vs. Glass vs. Filter Balls: What to Put in Your Sand FilterYour sand filter can run traditional sand, recycled glass, or poly-fiber filter balls. Glass is the upgrade most people should make; sand is the safe default; filter balls are the lightweight wildcard. The honest comparison.Pool Pump & Filter Troubleshooting: Won't Prime, High Pressure, Noises, No FlowA symptom-first troubleshooter — high pressure, no flow, won't prime, noises, drips, sand in the pool. The free fix first, the real part only when it's earned.Heat Pump vs Gas Pool Heater: What Each Costs to Run, With a CalculatorHeat for about half the price, or heat five times faster. The running-cost math with the energy prices stated, how far a heat pump really falls in cool air, and the install quote that decides most purchases.Why Isn't My Pool Heating? (Heater Basics + the No-Heat Checklist)Which heater fits your pool, the no-heat checklist (usually a free fix), sizing, and the one move that cuts heating cost 50–70%.Will a Pool Robot Wear Down Your Pool's Finish? (Vinyl, Fiberglass, Plaster)A well-matched robot won't wear your finish faster — how vinyl, fiberglass, and plaster differ, and why steps and shelves are about coverage, not wear.Pentair vs. Jandy vs. Hayward: You Are Picking a Platform, Not a BrandThe pump, filter, heater and light are not six decisions. The automation controller is one decision that makes the other five for you, because mixing brands demotes equipment to an on/off relay. And only one of the three sells you a way back out.Does a Pool Warranty Survive an Online Purchase? Heaters, Pumps and Salt ChlorinatorsBuy major-brand pool equipment online and the multi-year warranty usually isn't what you think. Heaters, pumps and chlorinators — verbatim terms, one dated table.Do Solar Pool Lights Actually Work? (And Why Yours Is Dim Under a Screen Cage)Solar pool lights work, within limits worth knowing before you buy: expect an evening rather than all night, expect less under a screen enclosure, and expect placement to matter more than price. The honest failure modes and the fixes that cost nothing.
Pool build & materials
How a Pool Gets Built, Start to Finish: Nine Stages, Four Inspections, and What Each One FreezesThe nine stages in order, the four inspections that gate them, and the moment each decision becomes permanent. Plus the rules worth writing into the contract, because the industry publishes three different pressure-test specs and no single one of them is the standard.Concrete (Plaster) vs. Fiberglass vs. Vinyl: The Honest Pool-Type ComparisonThe three ways to build a pool — concrete/gunite (plaster or aggregate finish), fiberglass, and vinyl-liner — compared honestly on durability, cleanability, longevity, maintenance, and cost. Plus the Florida water-table and saltwater factors.Diamond Brite vs. PebbleTec: They Are Not Competing FinishesTwo finishes people cross-shop that are not on the same rung. Diamond Brite is quartz, PebbleTec is pebble, and the price gap between two such bids should reflect a rung change rather than a brand preference.StoneScapes vs. PebbleTec: Ask Which StoneScapes FirstBoth are pebble finishes, so the brand is not the question. StoneScapes comes in three pebble sizes that map onto Pebble Technology three textures, and the two makers warranties are not close.Hydrazzo vs. PolishedScapes vs. Primera Stone: Three Polished Finishes, Three Different AggregatesAll three are polished. All three can be re-polished instead of replastered. But they polish marble, marble-and-glass and pebble respectively, and the hardest aggregate wins the wear surface.Sun Shelf, Bench, Bump-Out, Bar Stools, Steps and Stairs: The Concrete You Pour OnceSun shelf, bench, bump-out, built-in bar stools, a seating area with or without a table, and the entry steps — pool stairs, if that is what your builder calls them. All poured once, all permanent, all decided before gunite. And every one of them is specified from a datum or in a vocabulary the industry never agreed on.Spa or No Spa: What an Attached Spa Really Costs YouEvery builder will sell you a spa and none of them will show you a measured number, because for an attached spa no measured number exists. What it costs in swim length, in fuel, and in sightlines.Pool Water Features: Scuppers, Sheer Descents, Spillovers, Bubblers & Laminar JetsWhat each water feature is, where it goes, and the flow it needs — plus the units trap that makes published GPM figures look like they disagree when they don't.Fire Features for Pools: Fire Bowls, Fire-and-Water Bowls & Fire PitsFour things get called a pool fire feature and only one of them is furniture. What each costs to install rather than to buy, how much BTU it takes to actually feel warm, and what a screen cage does to the whole plan.Pool Cage Screen Types: Which Mesh Should Go in Your Enclosure (and What It Costs)Every pool-cage screen mesh compared — 18x14 standard, 20x20 no-see-um, Super Screen polyester, pet screen, Florida Glass, and solar (SunTex 80/90). Benefits, drawbacks, lifespan, and a real 2026 Florida cost comparison, with the panel-by-panel strategy most cages actually use.Pool Tile Types: Porcelain vs. Glass vs. Ceramic vs. Stone (and What Each Costs)Ceramic, porcelain, glass, stone, and mosaic pool tile compared honestly — look, durability, where each can go, and real 2026 cost. Porcelain is the value pick; glass is the splurge.Pool Deck Materials: Travertine vs. Pavers vs. Porcelain vs. Concrete (Heat, Slip, Salt & Cost)Travertine, limestone, shellstone, marble, concrete/brick and porcelain pavers, poured and stamped concrete, cool-deck coatings, flagstone, composite, wood, and artificial turf compared for a pool deck — heat underfoot, slip, salt, and real 2026 cost. The secret: color sets how much heat a deck absorbs, but the material decides how much it stores and how fast it burns bare feet.Pool Deck Care: Cleaning Algae and Sealing by Material (Travertine, Kool Deck, Pavers, Concrete)Clean and seal the deck around your pool by what it's made of: mild bleach is allowed on outdoor stone, acid is not; Kool Deck wants soap and a nylon broom; a glossy film turns slick wet; and a salt pool changes the sealer.You Just Filled Your Pool — What to Do Next (New Fill & New Plaster Start-Up)Two jobs, one phrase. The first-week checklist for any new fill, plus the high-stakes 30-day protocol for new plaster — and which start-up method actually protects the finish.Pool Coping Types: Bullnose vs. Eased Edge vs. Cantilever, Which Fits Your Pool, and Which Stone SurvivesBullnose, eased edge, square, drop-face, poured cantilever and rock coping compared — which ones a gunite, fiberglass or vinyl-liner pool can take, what the ISPSC requires, why the coping-to-deck joint is where coping fails, and how travertine, limestone, granite, porcelain, pavers, brick and concrete handle splash, salt and freeze.
Pool School is free and independent. When a fix genuinely needs a product — a real test kit, a robot that keeps up — we'll point you to the showdown, and we say so honestly. We never sell you a bottle you don't need. Here's what readers say after we've walked them through one of these.