Comparison
Compare the Fluval M Series wattage variants
The Fluval M Series is a family of submersible heaters, but the sizes are not a single interchangeable product. Fluval's US comparison table lists different wattages, aquarium capacities and heater lengths. Those are meaningful setup differences; review the exact item number before comparing an offer.
Manufacturer-listed M Series size differences
| Model | Power | Aquarium rating | Listed length | Manufacturer item no. |
|---|---|---|---|---|
| M50 | 50 W | Up to 15 US gal / 50 L | 11 in | A781 |
| M100 | 100 W | Up to 30 US gal / 100 L | 11 in | A782 |
| M150 | 150 W | Up to 45 US gal / 150 L | 13 in | A783 |
| M200 | 200 W | Up to 65 US gal / 200 L | 13 in | A784 |
| M300 | 300 W | Up to 80 US gal / 300 L | 15 in | A787 |
What this table cannot decide
A model's maximum aquarium volume does not guarantee that it will reach every requested temperature in every room. Fluval's M100 documentation, for instance, describes a limit on the room-to-setpoint difference and warns that colder rooms and other aquarium conditions can call for more heating capacity. Confirm the condition in the manual for the exact model you choose. Check tank volume, target temperature, room temperature, cover and water circulation rather than selecting watts from this table alone.
The table also does not establish product age, present retail stock, included accessories or the condition of any seller's package. Do not assume that the dimensions or heater guard of one size apply to another. Confirm the item number, wattage, package and current instructions before ordering.
Research status
This guide records the differences shown in Fluval USA's official M Series pages. All five exact M Series variants have individual fact dossiers, reviews and source-associated product visuals: M50 (A781), M100 (A782), M150 (A783), M200 (A784) and M300 (A787). The M50/M150/M200/M300 gallery views are official model-page thumbnails showing the heater body, not a package or scale reference; the M100 uses a larger studio image. Captions explain that scope, and none of these pictures establishes dimensions or heating performance. The reviews are linked here: M50, M100, M150, M200, M300. This comparison table is not a substitute for those individual assessments. The values come from Fluval's M100 family compare table and model links, not an independent heating test.