Help me choose
Our pick: Dolphin Sigma
Dolphin Sigma is the Pool Express pick in this matchup. Dolphin Sigma includes a 55 ft cable with anti-tangle swivel. Dolphin Sigma's documented advantages include standard filters and NanoFilters.
ProLine
Dolphin Sigma
Inground pools up to 50 ft that need floor, wall and waterline cleaning, with fine debris.
M-Line
Dolphin M400
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 M400: our take
Dolphin Sigma and Dolphin M400 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 M400 includes Standard filter and UltraFilter. Both have documented fine-debris media, so basket capacity and ease of cleaning matter more than fine-particle capability.
Controls and day-to-day ownership
Dolphin Sigma provides a weekly timer, smartphone control, and included remote control; Dolphin M400 provides smartphone control. Dolphin Sigma uses a 55 ft corded cable with an anti-tangle swivel, while Dolphin M400 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 M400 at $1,599; Dolphin M400 is $800 less. Each lists a 3-year manufacturer warranty. Pool Express pick: Dolphin Sigma. Dolphin Sigma includes a 55 ft cable with anti-tangle swivel. Dolphin Sigma's documented advantages include standard filters and NanoFilters. Choose Dolphin M400 when it is the better fit for shoppers prioritizing the lower $1,599 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 M400 |
|---|---|---|
| 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 | No |
| Automatic scheduling | Yes | Not listed |
| Smartphone app | Yes | Yes |
| Anti-tangle swivel | Yes | Yes |
| 3-year warranty | Yes | Yes |
| 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.
- 55 ft cable with anti-tangle swivel
- Standard filters and NanoFilters
Where Dolphin M400 stands out
Dolphin M400 is the better fit for shoppers prioritizing the lower $1,599 starting price.
- Is listed $800 lower
- 60 ft cable with anti-tangle swivel
Dolphin Sigma vs Dolphin M400 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 M400 |
|---|---|---|
| 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 | $1,599 |
| 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 | Standard filter, UltraFilter |
| Scheduling | Weekly schedule + app | Not listed |
| App and remote | App + included remote | App control |
| Cable | 55 ft with anti-tangle swivel | 60 ft with anti-tangle swivel |
| Robot weight | 24.6 lb | Not listed |
| Warranty | 3 years | 3 years |
Choose Dolphin Sigma
Dolphin Sigma is the Pool Express pick in this matchup. Dolphin Sigma includes a 55 ft cable with anti-tangle swivel. Dolphin Sigma's documented advantages include standard filters and NanoFilters.
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