Pool Chemistry 101: The Complete Beginner's Guide

Why Pool Chemistry Matters

A pool full of water looks refreshing, but without proper chemistry, it's a slow-growing ecosystem of bacteria, algae, and organic waste. Every time someone swims, they add body oils, sunscreen, sweat, and dead skin cells. Rain brings dirt and dilutes chemicals. Leaves and debris feed algae.

Pool chemistry isn't complicated once you understand what each piece does. This guide covers every major chemical, why it matters, and what to do when levels go off.

Start by testing your water. Scan your test strip in Pooli's Test Strip Scanning tool — it logs your readings and runs them through the Water Report to show you exactly what to add and how much.

The Six Tests Every Pool Owner Should Run

Before you reach for a single chemical, you need to know where your water actually stands. These six readings answer 99% of "what should I add?" questions.

Each of these gets its own deep dive below.

How to Actually Test — Three Methods, From Fastest to Most Accurate

You can't fix what you can't measure. The three testing methods below are the ones we recommend at Pooli, and you can scan results from any of them into the app.

1. Test strips (30 seconds, 5–7 readings at once)

Dip, hold for 15 seconds, compare colors. Strips read FC, pH, TA, CH, CYA, and sometimes bromine and total hardness in one shot.

The AquaChek 7-Way and Pooli's strips (included in Pool Club) are tuned for the Pooli SCAN reader. Open Pooli's Test Strip Scanning tool, photograph the strip, and Pooli reads every pad to within ±10% accuracy — better than the human eye can do against a printed color chart.

2. Liquid drop kits (the FAS-DPD standard, ~5 minutes)

Drop kits read free chlorine to a 0.2 ppm resolution — something strips physically cannot do. They're the standard for chasing algae problems, dialing in CYA, and troubleshooting weird readings.

The Taylor K-2006 kit is the industry standard. Test strips for daily checks, K-2006 for opening, closing, and any "why is this off?" moment. Snap the comparator tube into Pooli's Universal Test Scan and it logs each result.

3. Digital colorimeters (lab accuracy at home)

Devices like the LaMotte ColorQ 2X Pro 7 run the same chemistry as drop kits but read the results electronically — no eyeballing pink-vs-fuchsia. Pair it with Pooli over Bluetooth and every reading auto-imports.

If you have multiple pools, hot tubs, or a saltwater system you're really dialing in, the ColorQ is worth every penny.

Whichever method you pick, log every reading in Pooli. Trends matter more than any single reading — the Water Report uses 30 days of history to predict chemical demand.

Primary Sanitizer — Chlorine and Its Alternatives

Chlorine is the frontline defense against bacteria, viruses, and algae. It oxidizes contaminants by breaking into their molecular structure and destroying them. There is no "chlorine-free" pool that's actually sanitized — even saltwater pools generate their chlorine on-site.

Target range: 1–3 ppm free chlorine (or per the Chlorine/CYA Chart — see CYA section below)

Below 1 ppm your pool isn't being sanitized. Above 5 ppm it's harsh on skin, eyes, and swimsuits.

Chlorine product types

Every one of these has a different oz-per-1-ppm-FC ratio. In Pooli, you tell us your exact product (including custom "this jug is 8.25% sodium hypochlorite from Lowe's" levels) and we dose for that specific concentration — not a generic average.

Saltwater pools

A salt cell generates chlorine from dissolved salt (3,000–3,500 ppm). You manage cell output % and run time, not bottles of chlorine. Pooli tracks salt level, cell output, and lets you log boost mode runs.

Alternative sanitizers

Mineral systems, UV, and ozone reduce chlorine demand but do not replace chlorine — they let you run lower FC. Tell Pooli which supplemental system you use and the app lowers your FC targets automatically.

pH — The Master Knob

pH measures how acidic or basic your water is on a scale of 0–14. Pool water ideally mirrors the pH of human tears.

Target range: 7.4–7.6

• Too low (<7.2): Corrodes plaster, etches concrete, eats heater elements, irritates eyes
• Too high (>7.8): Chlorine loses up to 70% of its effectiveness, water turns cloudy, scale builds on tile and heater

Everything entering the pool affects pH — rain (acidic), swimmers (slightly basic), most chemicals (varies), and especially cal-hypo and soda ash additions.

• To raise pH: Soda ash (sodium carbonate) — fast-acting; or aerate with the spillover
• To lower pH: Muriatic acid (hydrochloric acid 14.5–31.45%) or dry acid (sodium bisulfate)

Pooli's Adverse Effects Warning stops you from overcorrecting pH when alkalinity is low — a common rookie mistake that causes pH to rebound by morning.

Total Alkalinity — The Buffer

Alkalinity stabilizes pH so it doesn't swing 0.4 units between morning and afternoon. Get TA right and pH largely takes care of itself.

Target range: 80–120 ppm (80–100 for SWG and high-pH source water)

• To raise TA: Baking soda (sodium bicarbonate, NaHCO₃). Pool-store "alkalinity increaser" is literally just baking soda at 3–4x the price.
• To lower TA: Muriatic acid added in one spot with the pump off, then aerated to drive off CO₂.

Always balance TA before pH — fixing TA usually moves pH in the right direction at the same time.

Calcium Hardness — Prevents Etching and Scale

Measures dissolved calcium. Both too low and too high cause problems.

Target range:

• 200–275 ppm for vinyl and fiberglass

• 200–400 ppm for concrete/plaster (the plaster needs the calcium or it leaches its own)

• Too low: Water is "hungry" and pulls calcium out of plaster, grout, and heater elements

• Too high: White flaky scale on tile, cloudy water, scaled heater

• To raise: Calcium chloride flakes

• To lower: Partial drain and refill (or a SC-1000 sequestrant as a temporary measure)

Cyanuric Acid — Chlorine's Sunscreen

CYA slows UV degradation of chlorine by roughly 3–5x. Without it, an outdoor pool can lose 90% of its FC in a single sunny afternoon.

Target range:

• 30–50 ppm for traditional chlorine pools
• 60–80 ppm for saltwater pools (the longer dwell time helps cell efficiency)

Trichlor tabs add ~3 ppm of CYA per ppm of FC delivered, so CYA tends to creep up all season. Track it monthly.

• Too low: FC burns off too fast; you're constantly adding more chlorine
• Too high (>90 ppm): Chlorine becomes progressively less effective ("chlorine lock") — the only fix is partial drain and refill. Phosphate-style "CYA reducers" rarely work.

Pooli's Water Report uses the Chlorine/CYA Chart to set your minimum FC target based on your actual CYA, not a one-size-fits-all 1–3 ppm.

TDS — The Health Check

Total Dissolved Solids is the sum of everything dissolved in your water — salt, calcium, CYA, leftover chemical byproducts, sunscreen residue, you name it.

Target range: < 2,000 ppm above your fill water (saltwater pools are typically 3,500–5,000 because of the salt itself)

When TDS climbs above ~2,500 ppm over fill, chlorine becomes less effective even when FC reads normal, water can feel "flat" or oily, and minor algae outbreaks become routine. The fix is a partial drain-and-refill (usually 1/3 of the pool).

Shocking — The Weekly Reset

Shocking adds a large dose of chlorine to oxidize chloramines (the "pool smell"), wipe out bacteria, and burn off organic buildup that daily FC can't catch.

• Routine shock: ~10 ppm FC (about 1 lb cal-hypo per 10,000 gallons, or 1 gallon of 12.5% liquid)
• Algae / SLAM: Raise FC to the SLAM-level FC for your current CYA — Pooli calculates this for you
• Shock at night — sunlight destroys unstabilized chlorine within hours. Run the pump overnight to distribute it.

Pooli's AI Algae & Cloudiness Scan lets you photograph a green or cloudy pool and returns an exact shock multiplier plus a step-by-step plan. As of v7.7.0 you can ask Percy follow-up questions to tailor the dose.

Specialty Chemicals — Use When Needed

The Right Order to Balance Water

This sequence is the difference between two test strips and a clean pool. Skipping ahead wastes chemicals and money.

1. Test everything first — scan a strip in Pooli (or pour a drop test, your call)
2. Adjust Total Alkalinity (baking soda or muriatic acid)
3. Adjust pH (if still needed after TA settles)
4. Adjust Calcium Hardness
5. Adjust Cyanuric Acid / Stabilizer
6. Adjust Free Chlorine (and add salt if you run an SWG)
7. Shock the pool (at night, if FC < target or chloramines > 0.5)
8. Retest after 24 hours

The Pooli Water Report runs this sequence automatically once your readings are in. It calculates exact doses for your product, your pool's volume, and your current numbers — and tells you what to add first and when to retest.

How Pooli Adapts to Your Specific Products

Most pool-care advice assumes you have generic 10% liquid chlorine and 100% pure baking soda. In reality, that 12.5% jug from Leslie's, the 8.25% Pool Essentials at Lowe's, and the 8% Clorox Pool & Spa all dose differently — sometimes by 30% or more.

In Pooli's inventory you can:

• Add a custom product with the exact active ingredient and concentration
• Pick that product for any addition and Pooli scales the dose precisely
• See adverse effects before you add (e.g. "this much cal-hypo will push your CH out of range")
• Track which jug, container, or bag the chemical came from — useful when you have multiple sheds, trucks, or pools

You can also tell Pooli that you run a supplemental sanitizer (UV, ozone, minerals) and your FC target drops automatically.

Quick Reference — Target Ranges

Tape this to the inside of your equipment shed door — or just let Pooli remember it for you.