If you own a hot tub and you've started shopping for a FROG system, you've hit the same wall everyone hits: there are two of them, they look similar, they cost about the same, and nothing on the box explains which one you should buy.
Here's the short answer. @Ease uses chlorine. Serene uses bromine. Everything else follows from that one difference.
What both systems have in common
Both are floating cartridge systems that sit in your hot tub and release sanitizer slowly, so you're not measuring and dosing chemicals by hand every few days. Both pair that sanitizer with a mineral cartridge, which does part of the sanitizing work on its own. That's the reason FROG water tends to feel softer and smell less chemical than a conventionally dosed tub — you're simply using less sanitizer to get the same result.
Both drop straight into the tub. No plumbing, no install, no equipment changes.
FROG @Ease: the chlorine option
@Ease uses SmartChlor, which is the genuinely clever part of the system. Instead of releasing chlorine on a fixed schedule, SmartChlor is self-regulating: it releases more when bather load goes up and throttles back when the tub sits unused. When the cartridge runs out, it stops releasing and the indicator turns white, so you get a visual cue rather than having to guess.
In practice that means less shocking, fewer surprises after a busy weekend, and water that stays consistent even if your usage is irregular.
@Ease suits you if: your tub usage varies week to week, you want the lowest-maintenance option available, or you simply prefer chlorine.
Spa FROG Serene: the bromine option
Serene uses bromine, and bromine has one real advantage in a hot tub: it holds up better at high temperatures. Chlorine burns off faster the hotter the water gets, which is why a 104°F tub is harder on chlorine than a 82°F pool. Bromine is more stable in that environment.
Bromine is also gentler on skin and produces less of the sharp smell people associate with chlorine. The trade-off is that it takes longer to re-establish after a heavy shock, and it costs a little more per season.
Serene suits you if: you run your tub hot, you use it frequently, or anyone in the household finds chlorine harsh on skin or eyes.
The mistake to avoid
The two systems are not interchangeable. An @Ease holder will not take Serene cartridges, and Serene refills won't fit an @Ease frame. If you already own one, buy refills for the system you have — the part number printed on your old cartridge is the fastest way to get it right.
It's also worth knowing that switching sanitizer type mid-season isn't as simple as swapping cartridges. Chlorine and bromine shouldn't be mixed in the same water. If you're changing from one to the other, do it at a water change.
How long the cartridges last
Mineral cartridges run up to six months on either system. That's the long-lived piece.
The sanitizer cartridges are the consumable you'll actually reorder. SmartChlor and Serene bromine cartridges are measured in weeks, not months, and the real lifespan depends on three things: how hot you keep the water, how often the tub is used, and how many people are in it. A tub used twice a month by two people will go through cartridges far more slowly than one used four nights a week by a family.
Don't guess — test. FROG test strips read sanitizer level along with pH and alkalinity, and take about fifteen seconds.
Why this matters more in fall and winter
Hot tub season runs opposite to pool season. Usage climbs as the weather cools, which means higher bather load, higher water temperature relative to the air, and faster sanitizer consumption — right when you're least inclined to stand outside fiddling with test kits.
That's the case for a floating system generally. Set it, check it weekly, and reorder cartridges before you run out rather than after.
Which to buy
If you're starting fresh and have no preference, most owners are happiest with @Ease, because SmartChlor's self-regulation removes the most common source of hot tub frustration: water that's fine one week and cloudy the next.
If you already know you prefer bromine, or chlorine bothers your skin, Serene is the better fit and you won't regret it.
Either way, buy the refills at the same time. Running out mid-winter is how a well-maintained tub turns cloudy.
Browse all FROG cartridges and refills or see the full hot tub and spa range.
