Pool care, from someone who assumes you have never done this

There are four numbers, and two of them matter most

Pool chemistry sounds like a subject. It is closer to a checklist. For a seasonal above-ground pool you are managing four readings, and a test strip gives you all of them in fifteen seconds.

Free chlorine is the sanitizer actually available to kill things, and the U.S. Centers for Disease Control publishes a minimum of 1 ppm for pools. pH is how acidic or basic the water is; the CDC’s published range is 7.2 to 7.8, and outside it chlorine either stops working or starts stinging eyes. Total alkalinity — how strongly the water resists pH swings — is the one beginners ignore and then fight all summer, because when alkalinity is low the pH will not stay where you put it. Cyanuric acid is chlorine’s sunscreen: some is essential outdoors, too much and your chlorine stops responding.

Get alkalinity right first, then pH, then chlorine. Doing it in the other order is why people find themselves adding chemicals every day and getting nowhere. The full walkthrough is in pH and alkalinity, and test strips covers what to measure with. If the problem runs the other way — water that keeps hazing over while pH climbs back after every correction — high alkalinity and cloudy water is the page for that, and it starts by checking whether yours is genuinely high.

The weekly routine, honestly

Ten minutes, twice a week, plus the pump running on a timer. Skim the surface before debris sinks, because floating leaves are easy and sunken leaves are not. Test the water. Add chlorine to hold the level rather than to rescue it. Brush the walls where the water line sits. Rinse or backwash the filter when the flow visibly drops.

And run the pump long enough. Filtration is time, not power: guidance for a full turnover on a seasonal pool is typically eight to twelve hours a day in the heat of summer. That is a real commitment and a real electricity bill, which is why we price it in the cost-to-run guide rather than pretending it is free.

Week three, when the water turns

Nearly every first-time owner gets a cloudy pool in the first month, and it is worth saying plainly that this is normal rather than a sign you have failed. Cloudiness has four usual causes and they are distinguishable: not enough free chlorine, pH drifted out of range, the filter is blocked or not running long enough, or early algae. Our cloudy water page is built as a decision tree rather than a list, because the fix depends entirely on which of the four you have.

If the water has gone green rather than milky, that is algae, and it is a different job with a different sequence — brush, shock, filter, and only then rebalance. Shock is the tool for both, and using it correctly mostly means using enough of it, once, rather than a little every day.

Chlorine, salt and what you will actually spend

For a seasonal above-ground pool, stabilized chlorine tablets in a floating dispenser is the default for a reason: it is cheap, it is forgiving, and it meters itself out slowly. Chlorine tablets covers what to look for, including the cyanuric acid question that catches people in a small pool that is never fully drained.

Salt systems come up constantly and are widely misunderstood — a saltwater pool is still a chlorine pool, it just generates the chlorine on site instead of you carrying it. Whether that is worth the hardware on a seasonal pool is genuinely arguable, and salt versus chlorine argues both sides with the numbers attached.

If you have never done any of this, start at the first-time owner guide, which is the shopping list and the first-month calendar in one place, then the beginner’s routine for the habit that keeps it clear.

The invisible problem: cyanuric acid

This deserves its own section because it is the one failure mode that is genuinely confusing rather than merely annoying, and cheap test strips do not even measure it.

Every trichlor tablet you drop in the dispenser carries cyanuric acid. Outdoors that is essential — without it, ultraviolet light destroys your free chlorine within hours. But unlike chlorine, cyanuric acid is not consumed. It accumulates, and it only leaves the pool when the water does. Past a certain concentration your free chlorine reading looks perfectly healthy while the chlorine itself cannot actually do anything, which is exactly the point at which people conclude that pool chemistry is impossible.

Small pools hit this faster, because there is less water to dilute it into. If you top up rather than drain, plan on a partial drain and refill at some point — there is no chemical that removes it. Read the level every few weeks on a seven-way strip, which is the entire reason we tell people not to economize on a five-way one.

What to ignore

The chemical aisle is large and most of it is not for a seasonal above-ground pool. You can skip metal sequestrants, enzyme treatments, phosphate removers and weekly scheduled shocking — all of which solve real problems that most seasonal pools do not have, and the last of which quietly creates the cyanuric acid problem above. What you cannot skip is running the pump long enough. Everything else here is recoverable if you miss a week; under-filtered water in summer heat goes from fine to unusable in about ten days.

The four things you will actually buy

Testing first: our test kit roundup covers strips against liquid reagent kits and which readings each one can be trusted for. Then delivery — a floating chlorine dispenser is what turns tablets into a steady dose rather than a spike. Then correction, where pH and alkalinity balancers matter far more than most people expect, because doing them in the wrong order means doing them twice. And finally insurance: an algaecide, which is a preventative you keep in the shed rather than a rescue you buy in a panic.

One problem sits outside that routine and gets treated with the wrong product more often than any other: staining on the liner. Metal stains and organic stains look similar and respond to opposite chemistry, and there is a free thirty-second test that tells you which one you have. Our stain remover roundup starts with the test rather than the shelf.

Two situations fall outside the standard routine entirely. If you fill from a well, a hose pre-filter takes the iron out before it can ever stain the liner — the only product on this site that prevents a problem rather than treating one. And if you own a spa as well as a pool, hot tub chemistry is a genuinely different discipline: a few hundred gallons at 102 degrees swings faster than anything in this hub.

Six newer pages fill in the gaps around those routines. Which shock to buy turns on what else it adds — calcium or stabilizer — and pool salt is a purity specification rather than a brand. When the water will not clear, floc or clarifier is decided by whether your filter can vacuum to waste at all. Borates hold pH still in a pool that keeps climbing; filling from a well is where liner stains come from; and draining a pool covers the two readings that only dilution will fix, and why a vinyl pool should never be emptied.

Three newer pages deal with testing and the weeks you are not here. Strips, drops or digital explains which method gives you a number and which gives you a color band — and that most digital testers do not measure chlorine at all. A week away is a setup problem rather than a chemistry one, and hard fill water changes which shock you should be buying.

Three pages answer questions the rest of this hub assumes you already know. Evaporation or a leak settles a dropping water level with a bucket and two pen marks, using published evaporation rates that run from a fifth of an inch a day in still air to over an inch at 10 mph. How long before you can swim is the one where every article answers in hours and every EPA label answers in parts per million — the label is the rule. And pool enzymes handle the oils and waterline rings chlorine is bad at, ranked on which makers actually publish a dose rate you can price a season from.

Two more pages, both about the gap between tests. Smart pool monitors are ranked on the thing the listings leave out — cassettes at about $20 every one to two months against a sensor swapped every two years — plus the 8-to-9-inch skimmer requirement that rules the best-known one out of most above-ground pools. And how often to change hot tub water is arithmetic rather than opinion: gallons divided by bathers divided by three, which on a 200-gallon inflatable tub lands at about two weeks.

And one page about the number almost every spa owner gets wrong. Hot tub rash is caused by a named organism rather than by chlorine or by the heat, and the CDC publishes a hot tub sanitizer range that is higher than the pool one quoted everywhere else on this site: at least 3 ppm chlorine, or 4 to 8 ppm bromine. The top of the pool range is the bottom of the spa range, which is where the problem usually starts. The page also explains why non-chlorine shock does not prevent it.

One more, for the tub rather than the pool. Hot tub aromatherapy looks like the softest subject on this hub and turns on two hard specifications: whether a product is oil-free, and whether its dose is published per gallon so you can scale it. One brand publishes the clearest oil-free wording in the category and no gallon basis at all. The other publishes a rate of one ounce per hundred gallons — then works its own example against a four-hundred-gallon spa, which is about twice what a four-person inflatable holds. Intex, meanwhile, does not publish a water capacity for any PureSpa model, so the number you are supposed to divide by is not published by the maker of the tub.