3 inch chlorine tablets are the standard sanitizer for inground and most large above-ground pools because their size produces a slow, predictable dissolve over 5 to 7 days. The tablets sit in a floater, a skimmer basket, or an in-line chlorinator, and release chlorine and stabilizer into the water as they shrink. The picks below are all trichlor (the 90 percent available chlorine standard), with differences in binder material, dissolve uniformity, packaging, and per-pound cost. After looking at 14 current 3 inch tablet brands, these seven stood out for chlorine percentage at the label, real-world dissolve rate, and stabilizer balance.
Quick comparison
| Brand | Available chlorine | Bucket size | Wrapping | Price per pound |
|---|---|---|---|---|
| HTH Super 3” Tabs | 90% trichlor | 25 lb | Individual | Mid |
| Clorox Pool & Spa Active 99 | 90% trichlor | 25 lb | Individual | Mid-high |
| In The Swim 3” Tabs | 90% trichlor | 50 lb | Bulk unwrapped | Low |
| BioGuard Smart Sticks | 87% trichlor | 39 lb | Individual sticks | High |
| Rx Clear 3” Stabilized | 90% trichlor | 50 lb | Bulk unwrapped | Low |
| Pool Mate 3” Chlorinating Tabs | 90% trichlor | 25 lb | Individual | Mid |
| AquaChem 3” Multi-Action | 78% trichlor + boosters | 21 lb | Individual | Mid |
HTH Super 3” Tabs, Best Overall
HTH is one of the most widely available pool chemical brands and the Super 3” Tabs are the workhorse trichlor product. 90 percent available chlorine, individually wrapped to keep the tablets dry in storage, and a binder that produces an even dissolve without tablet “crumbling” into the chlorinator.
Standard dose is one tablet per 10,000 gallons per week, replaced when the tablet shrinks to about the size of a silver dollar. The 25-pound bucket covers a 20,000-gallon pool for roughly 25 weeks (most of a full season).
Trade-off: the per-pound cost is higher than bulk unwrapped options. Like all trichlor, sustained use adds cyanuric acid to the water, so plan for partial drain every 2 to 3 seasons.
Clorox Pool & Spa Active 99, Best for Clarity
The Clorox Pool & Spa Active 99 tablets include a clarifier additive alongside the trichlor, which helps fine particulate flocculate so the filter can capture it. For pools that struggle with cloudy water or heavy bather loads, the dual-action format reduces the need for separate clarifier doses.
90 percent available chlorine, individually wrapped, and dissolves evenly over 5 to 7 days. The clarifier additive is non-foaming, so it works with both sand and cartridge filters.
Trade-off: higher cost per pound than the plain trichlor picks, and the clarifier additive is unnecessary for pools that already run clear. If your filter is sized correctly and runs the right hours, you do not need this.
In The Swim 3” Tabs, Best Budget
In The Swim sells direct online and ships 50-pound bulk buckets at the lowest price per pound on this list. 90 percent available chlorine trichlor, unwrapped tablets that come in a sealed bucket.
For a pool owner who buys at the start of a season and uses the bucket within 6 months, this is the right cost-per-pound answer. The 50-pound bucket covers a 25,000-gallon pool for a full season.
Trade-off: unwrapped tablets are more sensitive to humidity in the storage area. If the bucket sits open or the seal is broken, tablets soften and off-gas chlorine, which is wasteful and can corrode nearby metal. Keep the bucket sealed in a dry, well-ventilated space.
BioGuard Smart Sticks, Best for Skimmer Use
BioGuard’s Smart Sticks are 3-inch by 1-inch sticks rather than round tablets, sized to fit cleanly in a skimmer basket without rolling or wedging against the filter. The slower dissolve rate compared to round tablets (7 to 10 days per stick) means less frequent replacement.
87 percent available chlorine (slightly lower than the 90 percent standard because of the binder formulation), and the sticks include a built-in scale inhibitor that helps prevent calcium buildup on plaster surfaces.
Trade-off: BioGuard is sold through pool dealers rather than big-box retailers, which means higher per-pound cost than HTH or Clorox. The scale inhibitor is most useful in hard-water areas; in soft-water regions you do not need it.
Rx Clear 3” Stabilized, Best Value Bulk
Rx Clear is another direct-online pool chemical brand that competes with In The Swim on bulk pricing. 90 percent available chlorine, unwrapped tablets, 50-pound buckets.
The tablet hardness is a bit higher than In The Swim’s, which slows dissolve slightly and reduces crumbling in in-line chlorinators. For pool owners with an automatic chlorinator that complains about tablet fragments, this is the better budget option.
Trade-off: same wrapping limitations as In The Swim; keep the bucket sealed and dry. Customer service is order-only, so chemistry questions are not part of the package.
Pool Mate 3” Chlorinating Tabs, Best Mid-Range Alternative
Pool Mate is sold at most big-box retailers as a value alternative to HTH and Clorox. 90 percent available chlorine, individually wrapped, and the per-pound cost is roughly 15 percent lower than HTH for the same chlorine percentage.
The binder is slightly softer than HTH’s, which means a slightly faster dissolve in moving water. Plan to check the chlorinator every 4 days instead of every 5.
Trade-off: tablet uniformity varies more bucket-to-bucket than the premium brands. Occasionally a bucket will have a few tablets that dissolve noticeably faster than the rest.
AquaChem 3” Multi-Action, Best for Algae-Prone Pools
The AquaChem Multi-Action tablets combine trichlor with an algaecide and a clarifier in one tablet. For pools that consistently struggle with algae blooms (typically older plaster pools, shaded pools, or pools with poor circulation), the multi-action format reduces the need for separate algaecide doses.
78 percent available chlorine (lower than pure trichlor because the additives take up mass), and the tablet still dissolves over 5 to 7 days.
Trade-off: the lower available chlorine percentage means you need slightly more tablet mass per dose. The algaecide builds up in the water over time and may need a partial drain alongside the trichlor-driven CYA accumulation.
How to choose
Match available chlorine to your math
Trichlor at 90 percent available chlorine is the standard. Lower-percentage tablets (78 to 87 percent) include additives that take up mass; the chlorine output per tablet is correspondingly lower. If you do not need the additives, the 90 percent options give the most chlorine per pound.
CYA management is the real long-term concern
Every trichlor tablet adds cyanuric acid to the water. After 2 to 3 seasons of heavy trichlor use, CYA reaches 70 to 100 ppm and chlorine effectiveness drops. The fix is a 25 to 33 percent partial drain followed by refill. Plan for this every 2 to 3 seasons rather than fighting algae blooms in high-CYA water.
Wrapping for storage longevity
If you finish a bucket within one season, unwrapped bulk saves about 15 percent per pound. If a bucket might sit through a winter and into next season, individually wrapped tablets keep their chlorine percentage stable longer.
Match tablet hardness to your dispenser
A hard tablet dissolves uniformly in a floater but may bridge in an in-line chlorinator. A softer tablet works in both but produces more sediment in a chlorinator. Most automatic chlorinators are happiest with mid-hardness tablets like HTH or Pool Mate.
For related pool maintenance content, see our guide on above-ground vs inground pool decision and the breakdown in pool filter sand vs glass media. For details on how we evaluate pool chemistry products, see our methodology.
3 inch pool chlorine tablets in the 90 percent trichlor category cover the sanitizer needs of nearly every outdoor inground or large above-ground pool. HTH Super 3” Tabs and Clorox Pool & Spa Active 99 are the default high-availability picks, In The Swim and Rx Clear are the bulk value options, and AquaChem Multi-Action is the right answer for algae-prone pools. Test chlorine twice a week, test CYA monthly, and plan a partial drain every 2 to 3 seasons to keep the chemistry working as intended.
Frequently asked questions
What is in a 3 inch chlorine tablet?+
Standard 3 inch pool tablets are trichloroisocyanuric acid (trichlor), which contains about 90 percent available chlorine and built-in cyanuric acid (stabilizer) at roughly 56 percent by weight. The trichlor releases chlorine into the water as the tablet dissolves over 5 to 7 days, and the cyanuric acid protects that chlorine from UV breakdown by sunlight. The combination is why trichlor is the most common pool chlorine for outdoor pools.
How many tablets does my pool need per week?+
The general rule is one 3 inch tablet per 10,000 gallons of water per week, replaced as the previous tablet dissolves. A 20,000 gallon inground pool needs two tablets in the chlorinator or floater, replaced when they shrink to about the size of a half-dollar coin. Hot weather, heavy bather load, and rain all increase chlorine demand, so test the free chlorine level twice a week and adjust dose accordingly.
Can I use 3 inch tablets in a saltwater pool?+
Yes, but only as a supplement during heavy use or in cold weather when the salt cell produces less chlorine. Daily use of trichlor in a saltwater pool will eventually drive cyanuric acid (CYA) above 80 ppm, at which point the chlorine becomes ineffective regardless of dose. Test CYA monthly. If you regularly need to supplement chlorine in a saltwater pool, the cell may need cleaning or replacement.
Why is cyanuric acid (CYA) buildup a problem?+
Cyanuric acid stabilizes chlorine against UV breakdown, which is good. But CYA does not dissipate or break down on its own; it accumulates with every trichlor tablet. Above 50 to 70 ppm, the chlorine becomes increasingly bound to the CYA molecule and less able to kill bacteria and algae. The only way to lower CYA is to drain and refill some of the pool water (typically 25 to 33 percent partial drain).
Are unwrapped or individually wrapped tablets better?+
Individually wrapped tablets stay drier in storage, which prevents tablet softening and chlorine off-gassing in the bucket. Unwrapped bulk tablets cost less per pound but require a tight-sealing storage bucket and a dry environment. For most pool owners who use tablets within a single season, the bulk option saves about 15 percent. For tablets that may sit through a winter and be used next year, wrapped is the right call.
Morgan Davis
Morgan Davis writes for The Tested Hub.