Reviewed 2026-07-182 min read

Aquarium UV sterilisers: only the exposed water receives a dose

UV acts on organisms that enter the chamber and receive enough irradiation. It does not reach fish, substrate, glass or pipe surfaces outside that path.

Key points

Lamp power is not the delivered microbial dose.
Particles can shield organisms from radiation.
Clearing green water does not prove every pathogen is controlled.

Dose is intensity over exposure

Higher flow commonly reduces contact time. Water transmission, chamber geometry, sleeve deposits and lamp ageing all change delivered exposure, so a wattage-only comparison is incomplete.

UVC can injure eyes and skin. Operate only inside the closed housing with its safety instructions and never look at an energised germicidal lamp.

Define the target first

UV may reduce selected suspended microorganisms; it cannot treat life stages attached to fish or surfaces. It also cannot repair crowding, unstable water or disease introduced without quarantine.

Green-water clarification, microbial load reduction and multi-tank biosecurity are different objectives with different dose and turnover needs.

Situation	What to do	Why
Suspended green water	Correct-dose UV and clean sleeve	Cells circulate through the chamber
Visible disease on fish	Obtain target-specific diagnosis	Not every stage is waterborne
High particle turbidity	Improve upstream filtration	Shielding reduces exposure

Check the result

After correct-dose uv and clean sleeve, measure or observe Suspended green water again with the same method. Record Clearing green water does not prove every pathogen is controlled. as well; if neither changes as expected, revisit the diagnosis before adding another intervention.

Sources and scope

Sources include institutions, technical studies and manufacturers. Chezur separates established mechanisms from editorial decisions for home aquariums.