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What aquarium range does Finnex publish for the TH-300S?
Finnex lists the 300 W TH-300S for 40–80 US gallons. That is a range with a meaningful 40-gallon lower endpoint, not merely an 80-gallon maximum; the current numeric finder cannot express that floor, so the model is kept as a reference and not a match. Room-to-water temperature difference and the actual setup still matter.
Explore this need in the finder →Does the TH-300S include thermostat control?
No integrated controller is established for the standalone TH Series item: Finnex calls it a titanium tube only and says controllers are sold separately. A separate Deluxe Combo pairs a TH tube with an HC-820M controller, but that bundle must not be assumed to be the package shown in a tube-only listing. Confirm that the purchased tube and controller are compatible and follow the exact setup instructions.
Explore this need in the finder →Is the 300 W TH tube suitable for saltwater?
Finnex describes the TH titanium line as suitable for marine and freshwater aquariums. This supports a water-type claim, not a complete installation decision: the standalone tube still needs a separate compatible controller, and the reviewed sources do not verify a precise TH-300S immersion procedure or a specific retailer package.
Explore this need in the finder →What Finnex identifies in the 300-watt TH model
This is a source-based assessment of the Finnex TH-300S, not a claim of personal use, a performance test or an independent temperature measurement. Finnex's TH family page gives this exact model a 300 W rating, 120 V input, 2.7 A, a 0.75-inch diameter and a 10-inch tube length. The manufacturer assigns it a 40–80 US-gallon band. The lower endpoint matters as much as the familiar upper “up to” figure: a 30-gallon aquarium is outside the stated TH-300S range even though a maximum-only filter might otherwise treat it as suitable.
A separate Finnex combo table uses the code TH-0300S for a 300 W tube paired with an HC-820M controller, while the current TH comparison page calls the entry TH-300S. This appears to be a zero-padded naming difference within the same TH family and power tier, but a buyer should check the model printed on the actual box and heater rather than treating the older combo-table code as a confirmed SKU or UPC. The standalone Finnex Shop page groups 300, 500 and 800 W selections on one product page; it does not supply a visible retail item number for the 300 W option.
Why this tube is a different kind of purchase
Finnex explicitly labels the current TH offer as a titanium tube only and says controllers are sold separately. That changes the shopping task. A keeper cannot simply add this tube to an aquarium and rely on an internal thermostat, because the reviewed standalone offer does not document one. Finnex's separate Deluxe Combo page describes an HC-820M controller paired with TH tubes and says other controllers that accept three-prong heating elements can work. The two-page HC-820M manual, for that separate control unit, lists a 110–120 V supply, 49.9–94°F control range and 1000 W maximum load. Those are controller facts, not specifications built into the TH-300S and not proof that a particular separate controller is included.
For a real purchase comparison, the model number on the tube, controller compatibility, outlet and electrical label, and the exact contents of the package all need to line up. A listing that shows the same tube but omits the temperature controller is not equivalent to the Deluxe Combo. Finnex's combo page gives a specific pairing, but no exact TH-300S retail SKU, UPC or active offer was established here. Its separate current Shop page displayed the options as sold out at the time checked; that dated page state is not proof of discontinuation or a statement about other sellers.
Where the TH-300S sits in the TH range
Finnex gives the 300 W TH tube the line's shortest listed physical length, 10 inches, with the same 0.75-inch diameter as the larger TH-500S and TH-800S. The 500 W entry is 14 inches and 70–130 gallons; the 800 W entry is 16.5 inches and 140–265 gallons. This makes the 300 W version the most compact TH tube in the manufacturer's table, but it does not make it a small-aquarium heater: its published capacity band begins at 40 gallons.
The closest wattage comparison is Finnex's THD-300S. The family page rates that different model at 40–80 gallons too, but shows a narrower 0.62-inch diameter and 12.5-inch length. Finnex says TH uses longer quartz sleeves and coils than THD and promotes more surface area and reduced cycling stress; those are manufacturer design claims, not independently verified lifetime or heating results. The choice between the two cannot be reduced to the gallon label alone. Their tube construction and dimensions differ, and both still require a compatible external temperature controller when bought as heating elements.
Material, guard and operating caveats
Finnex describes the TH heater body as titanium, says the metal will not shatter like glass, and states the TH models come with a high-temperature guard. It also describes the line for freshwater and marine tanks. These statements support material, water-type and guard comparisons, but they do not specify a full installation route. The pages reviewed here do not give a TH-300S immersion mark, orientation, minimum clearance, dry-operation rule, cord routing or inline-filter permission. A photograph showing a guard is not an installation manual, and the controller manual is not a heater-element manual.
There is also an electrical wording discrepancy worth resolving at the point of purchase. The current TH family table pairs the model with 120 V and 2.7 A in separate columns. The Deluxe Combo page labels its wattage/current column “Amperage @115V,” then gives 2.7 A for the corresponding 300 W tube. I preserve both source statements rather than silently converting the current to another voltage basis. Check the exact label and controller instructions before sizing a circuit or mixing separate components. The source pages do not state a frequency for this item, so none is inferred.
Why this remains a reference, not a finder result
The 40–80-gallon rating is a two-sided range, while the current finder can enforce only its maximum. If it returned the TH-300S for a 20- or 30-gallon aquarium, it would disregard Finnex's lower boundary. Even at 40 gallons, the tube-only offer lacks an included controller and the available documentation here does not settle installation. Keeping the reviewed model in the library preserves the actual evidence without presenting an incomplete combination as ready to use.
The official Shop's four product images were inspected. They show the TH tube and guard from different angles, but none identifies a TH-300S wattage or exact package; the first image is also shared on a selector that offers three power sizes. No exact-model image is used for this assessment. Before considering a TH-300S, verify the 40–80-gallon guidance against the real setup, inspect the 120 V nameplate, obtain a compatible controller, and use the instructions supplied for the exact element/controller combination. The published wattage is not a promise that a given room, lid, circulation pattern or livestock target will reach a desired temperature.
Key specifications
Key details at a glance
| Rated heater power | 300 W |
|---|---|
| Supported water types | freshwater / saltwater |
| Electrical supply | 120 V |
Use the exact model’s instructions for operating limits, supplied equipment and version differences.
Sources for this review
Sources for this assessment
Check the complete aquarium setup
Use the finder to compare documented tank size, water type, installation and temperature-control fit. A match does not guarantee the keeper's species-specific target or measured performance.