This is a reference, not a shop. Nothing here is for sale, there is nothing to book, and no product is recommended by name. What you will find instead is the reasoning: the chemistry that decides whether your chlorine works, the arithmetic that decides whether your filter can keep up, and the diagnostic order that separates a two-day problem from a two-week one.
Start with the five keys
Pool care is often sold as a shelf of bottles. It is better understood as five interdependent jobs, and the reason most pools misbehave is that one of the five has quietly stopped being done. Water that is circulating, being filtered, physically cleaned, chemically balanced and regularly tested is very difficult to ruin. Water missing any one of those is difficult to rescue with the other four.
The single most common mistake is to treat a symptom without asking which key has failed. Cloudy water gets a clarifier when the real answer is that the pump runs four hours a day. Algae gets shocked repeatedly when the real answer is a pH sitting at 8.2, where chlorine is barely working. Start at the five keys and the rest of this handbook makes sense in a different way.
When something is wrong right now
If you have a specific problem, go straight to it. Each of these pages covers what the thing is, what causes it, how to prevent it, and how to treat it once it has arrived.
- Algae in swimming pools — green, small-cell green, mustard, black and pink growths, and why they respond so differently to the same treatment.
- Cloudy water — there is no single cause, which is exactly why it is so often mistreated. Sixteen of them, in diagnostic order.
- Chloramines and combined chlorine — the reason a pool can smell violently of chlorine while having almost none that works.
- Why chlorine will not stay in the water — pH, temperature, sunlight and stabiliser, and why adding more stabiliser is usually the wrong move.
- Pink slime — a bacterium, not an algae, and treated completely differently.
- White water mold — the tissue-paper growth that lives in the plumbing rather than the pool.
- Metal staining and coloured water — how a trace of copper or iron ends up on your walls, and on blonde hair.
Equipment and routine
The mechanical side is short and it is mostly about run time and honest maintenance rather than about buying anything.
- Filtration questions answered — sand, cartridge and DE, when to backwash, and why backwashing is not cleaning.
- How long to run the pump — turnover, temperature and the reason "eight hours" is a starting point rather than an answer.
- Circulation — dead spots, return aiming and why the water you can see is not the water with the problem.
- How to vacuum a pool — the whole procedure, including the air-lock step everyone skips.
- How automatic pool cleaners work — suction, pressure and robotic, and what each one is and is not good at.
Measurements and seasons
- Pool volume tables — gallons, litres and surface area for common aboveground and inground sizes, plus the formulas.
- Winterising checklist — the closing sequence for vinyl-liner pools, in order, with the freeze-damage traps flagged.
Hot tubs and spas
A spa is not a small pool. It holds a fraction of the water at twice the temperature with ten times the bather load per gallon, and everything that is slow in a pool happens in a spa within hours.
- Hot water care — the six habits that keep a spa healthy, and the drain-and-refill interval that most owners stretch too far.
- Foaming spa water — what foam actually indicates, and why defoamer treats the symptom.
How to use this handbook
Three habits will save you more money and more weekends than anything on these pages.
Test before you treat. Almost every expensive pool mistake begins with someone deciding what is wrong by looking at the water. Clear water can be badly out of balance; green water can have perfect balance and a dead pump. Sanitiser level, pH, total alkalinity and calcium hardness are four numbers, and without them you are guessing.
Balance before you sanitise. Chlorine at pH 8.0 is a small fraction as effective as the same chlorine at pH 7.4. Adding sanitiser to unbalanced water is the most common way to spend money and change nothing. The US Geological Survey's explanation of pH is a good non-commercial primer if the logarithmic scale is unfamiliar; a jump from 7.4 to 8.4 is a tenfold change, not a small one.
Read the label. Pool and spa sanitisers and algicides are regulated pesticides. In the United States, the directions on the container are legally enforceable, and the Environmental Protection Agency's explanation of pesticide labels sets out what each section of that label means. The dose on the bottle is not a suggestion, and it is also not a floor to be improved on.
A note on scope
This handbook covers residential pools and spas: vinyl-liner, fibreglass and plaster pools, and domestic hot tubs. It does not cover commercial or public aquatic facilities, which are subject to health codes, operator certification and record-keeping requirements that residential owners do not face. It offers no medical advice. Where water quality touches health — chloramine irritation, hot tub folliculitis, indoor air quality — the material here is general and informational, and a doctor is the right person to ask about symptoms.
Chemical safety deserves the same caution as chemistry. Pool chemicals are concentrated oxidisers and acids; several combinations of them are genuinely dangerous, and the general principles in the Occupational Safety and Health Administration's overview of chemical hazards apply just as much in a garage as in a plant. Never mix products in a bucket, never add water to acid, and store oxidisers and acids apart.