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What size aquarium does Finnex list for the THD-500S?
The exact THD-500S row is rated for 70–125 US gallons, making its 70-gallon minimum as important as its 125-gallon upper number. Because the current finder cannot apply that lower boundary, this reference model is not shown as a match even at the listed endpoints. Do not treat a capacity band as a guaranteed temperature result for a particular room or aquarium.
Explore this need in the finder →Is the THD-500S smaller than the TH-500S?
Finnex gives both models a 500 W rating but lists the THD-500S at 0.62 inch by 12.5 inches and the TH-500S at 0.75 inch by 14 inches. THD's published band ends at 125 US gallons, compared with 130 for TH. These are real specification differences, not evidence that one is the better heater for every tank; confirm the usable clearance and exact package.
Explore this need in the finder →Can the THD-500S regulate temperature on its own?
Finnex labels the Shop item as a heater element only and states controllers are sold separately. Its THD specification page does not provide a setpoint range for this element, so do not assign a controller's specifications to the THD-500S. Confirm the controller, electrical load, and model-specific installation instructions that accompany the actual offer.
Explore this need in the finder →Exact THD-500S identity and published limits
This is a source-based assessment of the Finnex THD-500S, not a claim of ownership, hands-on use, laboratory testing or independently measured aquarium performance. Finnex's model table identifies THD-500S as a 500 W titanium heater element and gives a 120 V row, 4.5 A, 0.62-inch diameter, 12.5-inch length and a 70–125 US-gallon band. The official Shop selector has a separate 500 Watt option with variant ID 51093135720747; the exact Shopify SKU is “THD-500s.” That lowercase terminal character differs from the family-table spelling, which is kept visible as a source-level naming difference. The variant's barcode is null, so no UPC is supplied here.
The 70–125 US-gallon figure is not simply a maximum. If the active finder only checked whether a model's maximum covered the aquarium, it could return the THD-500S below 70 gallons. That would contradict the lower end of Finnex's own band. The current matcher has no minimum-capacity operator in this questionnaire, so this model is preserved as a reference rather than treated as an eligible match. Even inside the published band, the numbers are not a promise that a given room, lid, water flow or starting temperature will reach a chosen temperature.
The closest comparison is TH-500S—not a generic 500 W heater
Finnex also lists a TH-500S at 500 W, but that is a separate configuration. Both model rows share the same wattage and a 70-gallon lower limit. The THD-500S is listed at 0.62 inch by 12.5 inches with a 125-gallon upper value; TH-500S is 0.75 inch by 14 inches with a 130-gallon upper value. The difference is meaningful for a tank with constrained tube space and for a buyer trying to honor the documented range. It is not enough by itself to say one model is a better fit for all 70–125 gallon tanks.
The source describes THD as titanium paired with an internal quartz sleeve. Finnex contrasts that compact design with the TH Series' longer quartz sleeves and coils. This distinction belongs to the family description; it is not evidence from a comparative durability test. Likewise, 12.5 inches is the listed heater length, not a required clearance, an immersion depth or an instruction to install the unit in a particular position. Check the exact model's directions and the space needed around the whole assembly.
The external controller changes the package decision
The THD Shop page states that its listing is for the heating element only and that controllers are sold separately. The THD-500S row does not show a thermostat range, integral setpoint adjustment, temperature display or included probe. A 500 W element should not be mistaken for a complete thermostat-controlled heater. A separate controller must be selected and checked against both the exact element and electrical load; the reviewed sources do not identify a THD-500S-specific controller bundle.
Finnex reports 120 V and 4.5 A in separate columns but does not explicitly say which reference condition applies to the current number. It provides no frequency value in this family table. These fields are therefore retained as written, not turned into a derived electrical rating. Before purchasing, inspect the heater label, controller nameplate, plug and exact package contents. Do not infer that a listing showing the tube also includes the controller or that a third-party controller's specifications belong to the element.
Evidence for construction and safety claims is bounded
The family page says THD units use titanium with an internal quartz sleeve and that every TH and THD heater comes with a high-temperature protective guard. Its shared titanium copy describes freshwater and marine use. These statements support the recorded materials, common guard and listed water types. They do not establish the complete assembly as shatterproof; the product description itself identifies quartz within the titanium element, and no impact testing is presented.
The current Finnex instructions index lists manuals for HMH, HMS and HPC heater families, among other items, but it does not list THD. That limited index check leaves a model-specific installation manual unresolved; it is not proof that instructions do not exist through another route. The public family and Shop pages do not state a safe orientation, exact submersion mark, dry-operation permission, clearance or inline-filter use. Those details should come from the instructions supplied for the actual element/controller combination rather than an unrelated Finnex manual.
Why the family image does not identify this wattage
The official Shop selector pairs a guarded tube image marked “COMPACT” with its 300 W, 500 W and 700 W choices. It is used here only as a THD-family visual, with a caption that warns it does not identify the selected wattage, exact assembly or package. It is not a THD-500S-specific photograph; the exact wattage/package image remains unverified.
This review documents a real 500 W THD option and separates it from the similarly named TH-500S. The evidence supports distinct size and capacity fields, an element-only package, a separately required controller, and a shared guard. It does not provide the lower-capacity matcher rule needed to keep 70 gallons as a hard boundary, the complete supply rating or exact installation instructions. Reference-only treatment preserves those facts without creating a recommendation that might fit the wrong tank or omit a required component. Before evaluating an offer, verify THD-500S versus TH-500S on the label, confirm the controller is a separate compatible item, confirm the full electrical information and manufacturer capacity band, and read the exact setup directions. This record does not make a stock or availability claim.
Key specifications
Key details at a glance
| Rated heater power | 500 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.