Almost every pool problem is a water chemistry problem wearing a disguise. Cloudy water, algae, itchy skin, stained plaster, a heater that keeps scaling up — chase them back far enough and you land on a number that drifted out of range.
We cover the chemistry the way a good service tech explains it at the equipment pad: what each number does, which ones matter most, what order to fix them in, and how much of what to add.
Something wrong right now? Work through it in two or three questions20 guides in this section
Start here
If you only read one page in this section, make it this one. Everything else here builds on it.
The five numbers that matter, the order to fix them in, and the doses that actually work. Written by people who've done this on real pools for 20 years.
Everything published on water chemistry, newest first.
Chlorine reading high? Make sure the test isn't lying, stop whatever is feeding it, and let the sun do the work. When a neutralizer is worth using.
Aeration, soda ash or baking soda: which one your test calls for, how much to add, and why pH below 7.0 takes far more than the rule of thumb says.
Borates slow pH creep and the labels claim algae suppression. What the EPA labels really say, how much to add, the pH catch, and why only draining removes them.
It raises alkalinity, not pH — which is why people add it, get the wrong result, and add more. How much to use, and when soda ash is the right product.
It is not algae, it has roots, and it builds a shell over itself. Why chlorine alone never touches it, and the brushing protocol that actually clears it.
The honest answer is not a number of hours. It is a chlorine reading — and knowing which one saves you a day of waiting or an evening of stinging eyes.
Muriatic acid or dry acid, how much to add, and why the pH you keep chasing back down is usually an alkalinity problem wearing a disguise.
Too low and the water eats your plaster. Too high and it scales everything. Targets by surface, how to raise it, and why lowering it means draining.
Every chlorine product adds something besides chlorine — stabilizer, calcium or salt. Pick the one whose leftovers your water can still absorb.
Iron, copper and manganese ride in on the fill water and stain the pool the moment you chlorinate. How to test first, and what a sequestrant cannot do.
Phosphates feed algae, but a high reading is not why your pool went green. What the number means and when removing it is money well spent.
Metal stains, organic stains and scale all look similar and need completely different treatments. Here's how to tell them apart.
Why two pools with identical test results behave completely differently, and how the saturation index ties all your numbers together.
That strong chlorine smell means you don't have enough chlorine, not too much. Here's what free, combined and total chlorine each tell you.
Six things turn pool water cloudy and only one of them needs clarifier. Work through them in this order and you'll fix it in a day instead of two weeks.
Shock isn't a product, it's a level. Here's how to work out the right target for your pool, how much to add, and why the bag instructions fail so often.
If you're adding acid every three days, you don't have a pH problem. Here's what alkalinity actually does and how to stop chasing the number.
Four types of pool algae, four different fights. How to identify what you've got, kill it properly, and stop it coming back in three weeks.
What CYA actually does to your chlorine, why 30-50 ppm is the sweet spot, and how to bring it down when tablets have run it up to 100.
For a typical chlorine pool: free chlorine 2–4 ppm (scaled to your CYA level), pH 7.4–7.6, total alkalinity 70–120 ppm, calcium hardness 200–400 ppm for plaster or 150–250 ppm for vinyl and fiberglass, and cyanuric acid 30–50 ppm outdoors. Salt pools run CYA a little higher, around 60–80 ppm.
Chlorine first if the water is unsanitary, then total alkalinity, then pH, then calcium hardness, then cyanuric acid. Alkalinity before pH matters because alkalinity is what keeps pH from bouncing — set the buffer before you fine-tune the number it protects.
Three usual suspects: cyanuric acid is too low so sunlight is burning it off, cyanuric acid is far too high so the chlorine you do have is chemically hobbled, or there is a live organic demand in the water — early algae, a heavy bather load, or debris breaking down in a corner the brush never reaches.
One short email with the seasonal jobs that matter, the fixes worth doing yourself, and the gear that earned its price.
Keep going
Pool problems rarely stay in one category. These are the ones that come up next.
Weekly, monthly and seasonal pool maintenance done properly — brushing, vacuuming, filter cleaning and the routines that keep water clear with less work.
14 articlesExploreStep-by-step pool guides for owners at every level — from your first week with a pool to the jobs most people pay a service company to handle.
4 articlesExplorePumps, filters, heaters, salt cells, automation and lighting — how each one works, how to size it correctly and what actually justifies the upgrade.
18 articlesExplore