Indicator Lights & Sounds — Complete Reference GuideUpdated 2 months ago

This guide covers every LED and audible signal on the aF4 so you can understand exactly what your unit is telling you at a glance.

Power / Status LED

Located above the power button. This is the first LED to check when diagnosing any issue.

LED state	What it means
Off	No power — unit is not connected to power
Solid red	Power connected, unit is off
Flashing green	Unit is powering up
Solid green	Unit is on and operating normally
Flashing red	TEC (cooling element) damage detected — see below

Flashing red power LED — important: A flashing red power LED (ONLY the red power LED) is a separate fault from the flashing temperature LEDs. It indicates damage to the TEC (thermoelectric cooling element) and is not the same as an over-temperature event. If you see a flashing red power LED with no flashing temperature LEDs, submit a support ticket — this requires warranty assessment.

Temperature Row LEDs

The row of 5 green LEDs displays your current temperature setting during normal operation. The number of LEDs lit indicates which of the 5 temperature settings is active, with the leftmost (snowflake) being the coldest and the right the warmest. Snowflake is typically between -1.0C and 0C while setting 5 is typically between 4C and 5C.

LED state	What it means
1–5 LEDs lit steadily	Current temperature setting (leftmost = coldest)
All 5 flashing simultaneously	Over-temperature fault triggered

All 5 flashing is the only fault state for these LEDs. For a full explanation of what triggers this and how to resolve it, see our Blinking LED Guide and Over-Temperature Fault: Remedies & Prevention Guide.

Feed Time Offset LEDs

This row of 5 LEDs shows the current feed time offset setting. The aF4 feeds automatically once every 24 hours at the time it was powered on. The offset allows you to shift that feed time earlier or later without the use of an aquarium controller.

LEDs lit	Offset	Effect
1 (leftmost)	−4 hours	Feeds 4 hours earlier than power-on time
2	−2 hours	Feeds 2 hours earlier than power-on time
3 (center)	0 — default	Feeds at power-on time
4	+2 hours	Feeds 2 hours later than power-on time
5 (rightmost)	+4 hours	Feeds 4 hours later than power-on time

Note: Connecting anything to the link port (such as a smart controller) overrides the automatic 24-hour feed schedule. Feed timing will then be controlled by the connected device.

Feed Quantity LEDs

This row of 5 LEDs shows the current feed quantity setting. The number of LEDs lit indicates the selected portion size.

LEDs lit	Feed quantity
1	5 mL
2	10 mL
3	20 mL
4	30 mL
5	50 mL

Note: 5 mL is approximately equivalent to 85–100% of a single frozen food cube.

Link / Connectivity LED

Located on the top right of the aF4. This LED indicates the status of the link port connection.

LED state	What it means
Off	No device connected to the link port
Solid	Device connected and communicating normally
Flashing green	Feed signal is actively being received from a connected controller

When a controller such as the Neptune Apex, Coralvue Hydros, or GHL Profilux sends a feed signal via the 0-10v link port, the link LED will flash green to confirm the signal is being received.

Note: The flashing link icon behavior is only present on later 60XXX and 100XXX serial numbers.

Auto-Clean Button LED

The Auto-Clean button has a built-in LED that illuminates while an auto-clean cycle is actively running. It turns off when the cycle is complete. To activate the auto-clean cycle, press and hold firmly for 15 seconds or until you hear the clean cycle begin to operate.

LED state	What it means
Off	No auto-clean cycle running
Solid	Auto-clean cycle in progress

Do not activate Auto-Clean while the output tube is directed into the aquarium. Always redirect the output tube to a drain or container before running a clean cycle.

Audible Sounds

Auto-Clean completion beep: The aF4 emits three beeps when an Auto-Clean cycle has finished. This confirms the cycle completed successfully.

Continuous beep — over-temperature fault (serial numbers 100XXX only) Units with serial numbers beginning 100XXX emit a continuous beep when the over-temperature sensor is activated. This beep accompanies the flashing temperature LEDs and serves as an additional alert. Units with serial numbers beginning 20XXX or 60XXX do not emit this beep — they display the flashing LED error only.

Quick reference — all LED states at a glance

LED	Normal state	Fault / alert state
Power / status	Solid green	Flashing green (powering up) · Solid red (off, power connected) · Flashing red (TEC damage)
Temperature row (x5)	1–5 lit steady (shows setting)	All 5 flashing (over-temperature fault)
Feed time offset (x5)	1–5 lit steady (shows offset)	N/A
Feed quantity (x5)	1–5 lit steady (shows quantity)	N/A
Link / connectivity	Off or solid	Flashing green (feed signal received — normal)
Auto-Clean	Off	Solid (cycle running — normal)

Blinking LED Guide — detailed explanation of the over-temperature fault
Over-Temperature Fault: Remedies & Prevention Guide — how to resolve the fault
Power Issues Guide — if the power LED is not behaving as expected
UI Programming: Feed Time Setting — how to adjust the feed time offset
UI Programming: Feed Quantity — how to adjust the feed quantity

Something not covered here? Submit a ticket and our team will help.

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