Help me choose
Our pick: Dolphin Sigma
Dolphin Sigma is the Pool Express pick in this matchup. Dolphin Sigma carries a 3-year warranty instead of 2 years. Dolphin Sigma includes a 55 ft cable with anti-tangle swivel.
ProLine
Dolphin Sigma
Inground pools up to 50 ft that need floor, wall and waterline cleaning, with fine debris.
T-Line
Dolphin T55i
Inground pools up to 50 ft that need floor, wall and waterline cleaning, with fine debris.
Why Dolphin Sigma is our pick
Dolphin Sigma
Inground pools up to 50 ft that need floor, wall and waterline cleaning, with fine debris.
$2,399
Buy Dolphin SigmaDolphin Sigma or Dolphin T55i: our take
Dolphin Sigma and Dolphin T55i are compared on pool fit, cleaning reach, debris handling, controls and ownership details. The recommendation is based on the job the robot must do—not a simple feature count.
Pool fit and cleaning reach
Both robots are intended for inground pools. Both are rated for pools up to 50 ft. Each cleans floor, walls, and waterline, so coverage alone does not separate them. Dolphin Sigma's documented cleaning system includes 2 active brushes, SmartNav 3.0 with gyroscope navigation, and Triple commercial-grade DC motors.
Filtration and debris
Dolphin Sigma includes Standard filter and NanoFilters; Dolphin T55i includes Basket and UltraFilter. Both have documented fine-debris media, so basket capacity and ease of cleaning matter more than fine-particle capability. Dolphin T55i has the better documented path for bulky leaves and larger debris.
Controls and day-to-day ownership
Both models provide a weekly timer, smartphone control, and included remote control. Dolphin Sigma uses a 55 ft corded cable with an anti-tangle swivel, while Dolphin T55i uses a 60 ft corded cable with an anti-tangle swivel.
Price, warranty and the decision
Dolphin Sigma is listed at $2,399 and Dolphin T55i at $1,699; Dolphin T55i is $700 less. Dolphin Sigma lists a 3-year warranty compared with 2 years for Dolphin T55i. Pool Express pick: Dolphin Sigma. Dolphin Sigma carries a 3-year warranty instead of 2 years. Dolphin Sigma includes a 55 ft cable with anti-tangle swivel. Choose Dolphin T55i when it is the better fit for shoppers prioritizing the lower $1,699 starting price.
Feature check: what each robot actually has
A green check means the feature is documented as included. A red X means it is documented as absent. A dash means the source does not make the feature clear.
| Feature | Dolphin Sigma | Dolphin T55i |
|---|---|---|
| Cleans the pool floor | Yes | Yes |
| Climbs and cleans walls | Yes | Yes |
| Scrubs the waterline | Yes | Yes |
| Fine-debris filter included | Yes | Yes |
| Large-debris filter | No | YesEdge |
| Automatic scheduling | Yes | Yes |
| Smartphone app | Yes | Yes |
| Anti-tangle swivel | Yes | Yes |
| 3-year warranty | YesEdge | No |
| No recharging between cycles | Yes | Yes |
| Built-in UV-C water treatment | No | No |
Unknown is not treated as “no.” Specifications come from the product pages, current catalog records and manufacturer material collected for this site.
Where Dolphin Sigma stands out
Dolphin Sigma is the better fit for inground pools up to 50 ft that need floor, wall and waterline cleaning, with fine debris.
- Carries a 3-year warranty instead of 2 years
- 55 ft cable with anti-tangle swivel
Where Dolphin T55i stands out
Dolphin T55i is the better fit for shoppers prioritizing the lower $1,699 starting price.
- Includes a large-debris bin or bag for leaves
- Is listed $700 lower
Dolphin Sigma vs Dolphin T55i specifications
Use pool fit first. Price and app control do not make up for a robot that cannot cover the length or surfaces you need cleaned.
| Specification | Dolphin Sigma | Dolphin T55i |
|---|---|---|
| Best fit | Inground pools up to 50 ft that need floor, wall and waterline cleaning, with fine debris. | Inground pools up to 50 ft that need floor, wall and waterline cleaning, with fine debris. |
| Starting price | $2,399 | $1,699 |
| Pool type | Inground | Inground |
| Maximum pool length | Up to 50 ft | Up to 50 ft |
| Cleaning coverage | Floor, Walls, Waterline | Floor, Walls, Waterline |
| Power | Corded | Corded |
| Filtration | Standard filter, NanoFilters | Basket, UltraFilter |
| Scheduling | Weekly schedule + app | Weekly schedule + app |
| App and remote | App + included remote | App + included remote |
| Cable | 55 ft with anti-tangle swivel | 60 ft with anti-tangle swivel |
| Robot weight | 24.6 lb | Not listed |
| Warranty | 3 years | 2 years |
Choose Dolphin Sigma
Dolphin Sigma is the Pool Express pick in this matchup. Dolphin Sigma carries a 3-year warranty instead of 2 years. Dolphin Sigma includes a 55 ft cable with anti-tangle swivel.
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