Domakihub How to Choose Pool Chlorine Tablets: The Practical Guide
Pick the right size, strength, and delivery method so your pool stays clear all season.
Reviewed by Domakihub pool pros · 2026-06-23 · 5 min read
Chlorine tablets are the most convenient way to keep a pool sanitised, but buying the wrong type can quietly damage your water chemistry, corrode fittings, or leave swimmers with stinging eyes. The video above walks through the main delivery methods; this guide adds the buying criteria and step-by-step selection process tailored to the pools common across Greek homes, holiday villas, and hotel rooftops — where high summer temperatures and heavy bather loads make the right choice even more important.
Why tablet choice matters more in Greece
Greek summer sun is intense — UV radiation destroys unprotected chlorine in hours. Most chlorine tablets sold for outdoor pools are stabilised with cyanuric acid (CYA), which slows this breakdown significantly. However, if you top up tablets week after week without monitoring CYA levels, you can reach the point where the chlorine cannot work properly even though test strips show it is present. Understanding what is inside each tablet before you buy prevents this common trap.
A secondary concern unique to the Greek season is bather load. A private villa pool used by eight guests on a hot August day needs far more active chlorine than the same pool used by a retired couple in May. The tablet format you choose determines how quickly you can raise or adjust the dose.
Tablet sizes and what they are for
The market offers two standard sizes: 20-gram (1-inch) mini tablets and 200-gram (3-inch) standard tablets. Mini tablets dissolve quickly and suit small above-ground pools or spa pools under 5,000 litres. They are also useful for a precise boost mid-week without committing a large dose. Standard 3-inch tablets dissolve slowly over five to seven days and are the workhorse for in-ground pools of any size found in a Greek garden, courtyard, or rooftop. Never mix sizes in the same feeder — the chemistry balance is designed around one or the other.
5 steps to choose the right chlorine tablets
- 1
Measure your pool volume first
Every dosing decision starts here. For a rectangular pool, multiply length by width by average depth (in metres) and multiply by 1,000 to get litres. For irregular shapes, break the pool into sections. Write the figure down and keep it with your test kit — you will use it every time you buy tablets or add chemicals.
- 2
Decide: stabilised or unstabilised
For any outdoor pool in Greece, choose stabilised trichlor tablets (look for 'cyanuric acid' or 'CYA' on the label). They resist UV breakdown and cost less to maintain over a season. Only choose unstabilised (calcium hypochlorite granules or dichlor) tablets if your CYA reading has crept above 80 ppm and you need to chlorinate without adding more stabiliser.
- 3
Check the active chlorine percentage
Quality tablets list 'available chlorine' on the packaging. Aim for at least 87–90% available chlorine. Cheaper tablets from unknown brands often contain fillers that lower this percentage and leave scale or residue in feeders. A higher active-chlorine percentage means fewer tablets used per week, so the higher upfront cost often balances out.
- 4
Pick the right delivery method for your setup
Floating dispensers are the cheapest entry point but can bleach vinyl liners and bump into swimmers. An inline or offline automatic chlorinator attached to the return pipe is the cleanest method for in-ground pools and allows precise flow-rate control. Skimmer baskets can hold tablets in a pinch, but this pushes highly acidic water directly through the pump and can corrode seals over time — use it only as a short-term fix.
- 5
Test and adjust within 48 hours of adding tablets
After placing a fresh batch of tablets, retest your water the following morning. Check free chlorine (target 1–3 ppm), pH (7.2–7.6), and CYA (target 30–50 ppm for an outdoor Greek pool). If CYA is already above 70 ppm, partially drain and refill before adding more stabilised tablets. A simple four-in-one test strip takes under a minute and prevents the expensive chemistry corrections that come from ignoring this step.
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FAQ
- How many 3-inch tablets does a 50,000-litre pool need per week?
- As a starting point, use one 200-gram tablet per 25,000–30,000 litres of pool water per week under normal bather loads. For a 50,000-litre pool that means two tablets per week in a floating dispenser or chlorinator. Adjust up during heat waves or after heavy use and always confirm with a test — dosing by volume alone is a guide, not a guarantee.
- Can I use the same tablets in a spa or hot tub?
- No. Standard 3-inch trichlor tablets are too slow-dissolving and too concentrated for a spa's small water volume. The high heat also accelerates chlorine demand unpredictably. For spas use 1-inch mini tablets or dichlor granules designed for spas, and test the water before every use given the much higher bather-to-water ratio.
- My water is clear but guests still complain of red eyes — is it the chlorine?
- Red eyes are almost always a sign of incorrect pH rather than too much chlorine. If pH drops below 7.0, chlorinated water becomes acidic and irritating. Check pH first and adjust upward with sodium carbonate (soda ash) before blaming the chlorine level. Ironically, very high chloramine levels (not free chlorine) can also cause irritation — a sign you need to shock the pool, not reduce tablet dosing.