Help me choose
A stronger Pool Express option
Dolphin M400 and Dolphin Nautilus AG are compared feature by feature below. For a stronger Pool Express option, consider Dolphin Cayman. Inground and above-ground pools up to 40 ft that need floor and wall cleaning.
M-Line
Dolphin M400
Inground pools up to 50 ft that need floor, wall and waterline cleaning, with fine debris.
Nautilus
Dolphin Nautilus AG
Above-ground and small inground pools up to 30 ft that need the floor vacuumed.
What we recommend instead
Dolphin Cayman
Inground and above-ground pools up to 40 ft that need floor and wall cleaning.
$1,079
Buy Dolphin CaymanDolphin M400 or Dolphin Nautilus AG: our take
Dolphin M400 and Dolphin Nautilus AG 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
Dolphin M400 is intended for inground pools, while Dolphin Nautilus AG is intended for above-ground pools. Dolphin M400 is rated for pools up to 50 ft; Dolphin Nautilus AG is rated up to 30 ft. Dolphin M400 cleans floor, walls, and waterline; Dolphin Nautilus AG cleans floor. Dolphin Nautilus AG's documented cleaning system includes 1 active brush and CleverClean navigation.
Filtration and debris
Dolphin M400 includes Standard filter and UltraFilter; Dolphin Nautilus AG includes Basket. That gives Dolphin M400 the clearer documented edge for fine silt, pollen and sand. Dolphin Nautilus AG has the better documented path for bulky leaves and larger debris.
Controls and day-to-day ownership
Dolphin M400 provides smartphone control; Dolphin Nautilus AG provides one-touch starts and power-supply controls. Dolphin M400 uses a 60 ft corded cable with an anti-tangle swivel, while Dolphin Nautilus AG uses continuous corded power.
Price, warranty and the decision
Dolphin M400 is listed at $1,599 and Dolphin Nautilus AG at $568; Dolphin Nautilus AG is $1,031 less. Dolphin M400 lists a 3-year warranty compared with 1 years for Dolphin Nautilus AG. Dolphin M400 and Dolphin Nautilus AG each have a specific fit, but neither is the Pool Express pick for this job. Our better alternative is Dolphin Cayman. Inground and above-ground pools up to 40 ft that need floor and wall cleaning.
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 M400 | Dolphin Nautilus AG |
|---|---|---|
| Cleans the pool floor | Yes | Yes |
| Climbs and cleans walls | YesEdge | No |
| Scrubs the waterline | YesEdge | No |
| Fine-debris filter included | YesEdge | No |
| Large-debris filter | No | YesEdge |
| Automatic scheduling | Not listed | No |
| Smartphone app | YesEdge | No |
| Anti-tangle swivel | YesEdge | No |
| 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 M400 stands out
Dolphin M400 is the better fit for pools up to 50 ft.
- Cleans the floor, walls and waterline instead of stopping below the tile line
- Includes filtration for sand, pollen and other fine debris
- Adds smartphone control
- Uses an anti-tangle swivel cable
Where Dolphin Nautilus AG stands out
Dolphin Nautilus AG is the better fit for shoppers prioritizing the lower $568 starting price.
- Includes a large-debris bin or bag for leaves
- Is listed $1,031 lower
Dolphin M400 vs Dolphin Nautilus AG 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 M400 | Dolphin Nautilus AG |
|---|---|---|
| Best fit | Inground pools up to 50 ft that need floor, wall and waterline cleaning, with fine debris. | Above-ground and small inground pools up to 30 ft that need the floor vacuumed. |
| Starting price | $1,599 | $568 |
| Pool type | Inground | Above-ground |
| Maximum pool length | Up to 50 ft | Up to 30 ft |
| Cleaning coverage | Floor, Walls, Waterline | Floor |
| Power | Corded | Corded |
| Filtration | Standard filter, UltraFilter | Basket |
| Scheduling | Not listed | One-touch start |
| App and remote | App control | Power-supply controls |
| Cable | 60 ft with anti-tangle swivel | Not listed |
| Robot weight | Not listed | 14.6 lb |
| Warranty | 3 years | 1 years |
Consider the stronger Pool Express option
Dolphin M400 and Dolphin Nautilus AG are compared feature by feature below. For a stronger Pool Express option, consider Dolphin Cayman. Inground and above-ground pools up to 40 ft that need floor and wall cleaning.
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