Check the mounting span
Use the fixture’s published size range and mounting instructions. Measure the exact tank rim or mounting points, rather than assuming a nominal aquarium volume corresponds to a particular fixture length. A clip-on light has different mounting constraints from a fixture resting across two ends.
Leave access for feeding, the lid and equipment maintenance. Check the intended position of controls and cables before treating a fixture as a fit.
Check the lid ledge, brace and rear openings before choosing a mount.
Keep model generations separate
Fluval Plant 4.0 and Plant 3.0 are separate generations, with different item numbers and feature details. The light catalog retains them separately. A retailer photo or listing for one generation does not identify the other.
Similarly, two sizes in the same family can change power draw, mounting range and output. Choose the exact wattage and size record before using it in a plan.
Power is not a plant-light measurement
Watts help estimate electricity. They do not tell you how much plant-usable light reaches a leaf. Where the manufacturer supplies PAR, keep the measurement distance and conditions attached to the value.
Do not compare an unstated PAR value with one taken at a specified depth. Do not infer performance at a deeper substrate by scaling watts. Plants, shading, layout and the light schedule add questions beyond fixture dimensions.
Check the controls you will use
Find out whether normal setup requires an app, Bluetooth, a compatible phone or a separate controller. Verify which functions remain available without the app and how the schedule behaves after power is interrupted.
Record the planned daily schedule in the electricity calculator. Its hours are an editable cost assumption, not a recommended lighting duration for every planted tank.
Read water-resistance claims precisely
An IP rating describes a specified protection classification. It does not remove installation instructions, authorize unsupported submersion or make a power supply waterproof. Keep the fixture, supply and cable requirements separate.
Before purchasing, confirm the current model manual, tank mounting span, required controller and relevant published light measurements.