Photo: Netha Hussain · CC0
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Aquarium LED light for 10- and 20-gallon tanks
Six to eight hours on a timer beats leaving the kit hood on all evening. A full-length LED bar sized to the tank is the usual upgrade for planted 10s and 20s, not a reef-blast fixture and not a ranked light list.
Photoperiod first, fixture second
Fish do not need fourteen hours of daylight on a bookshelf. Six to eight hours on a timer is the default for a beginner community or a low-tech planted 10 or 20. More light without plants that actually grow, and without a fertilizer plan, mostly grows algae. Green water and hair algae problems often start as 'I left the light on.'
A timer, built into the fixture or a cheap outlet timer, matters more than chasing kelvin numbers. Consistency beats a bright light you forget to switch off.
Size the bar to the glass
A standard 10-gallon is about 20 inches long. A 20-gallon long is about 30 inches; a 20 high is closer to 24. Buy a full-length LED bar with adjustable brackets that sit on the rim or lid, not a clip-on night-light meant for a nano corner. Kit hoods are often dim, bluish, and uneven, a bar sized to the tank is the usual upgrade.
You do not need a reef-blast fixture on a betta 10 or a cherry-shrimp colony. Even, white-ish light you can look at without squinting is enough for fish color and easy plants (anubias, java fern, moss). High-PAR and pressurized CO2 belong in a dedicated high-tech build, for the beginner path, see the low-tech planted aquarium guide.
Algae, lids, and honesty
If the glass goes green two weeks after you upgrade the light, shorten the photoperiod before you buy another bottle of algae fix. Feed less, change water, and give plants time. Shrimp and otos help after those levers, not instead of them.
Keep fixtures dry: drip loops, lids when the maker says so, and no saltwater splash on indoor electronics. The picks below are an 18–24 inch timed bar for 10s, a 24–30 inch timed bar for longer 20s, and a mechanical outlet timer for hoods that only switch on and off. We may earn a commission if you buy. See the affiliate disclosure.
What we would buy
NICREW ClassicLED Plus, 18–24 inch
Full-length bar with adjustable brackets for a standard 10-gallon (20-inch) footprint, built-in timer, and white-forward light you can look at without squinting. Enough for fish and low-tech plants without a high-PAR reef blast.
Set 6–8 hours, not the longest preset. Use over a glass or acrylic lid when the maker recommends it. Skip this if a working hood already covers the tank and you only need a timer.
See this listingNICREW ClassicLED Plus, 24–30 inch
The step-up for a 20-gallon long or similar length. Same timer-and-spectrum idea as the smaller Plus, sized so the ends of a 24–30 inch tank are not dark corners.
Confirm your tank's outside length before you buy. A 20-high may want the shorter bar instead. Still a low-to-medium planted fixture, not a CO2 high-tech light.
See this listingBN-LINK 24-hour mechanical outlet timer
For kit hoods and simple LEDs that lack a built-in schedule. Peg 6–8 hours on, every day, so algae does not win because the light sat on overnight.
Grounded indoor timer. Put a drip loop in the cord. Skip stacking this on a fixture that already has a programmable controller, cutting power resets some digital timers.
See this listing
Frequently asked questions
How many hours should an aquarium light stay on?+
Six to eight hours on a timer is the default for a beginner community or low-tech planted tank. Longer photoperiods without plants and fertilizer usually grow algae, not healthier fish.
What size LED for a 10-gallon tank?+
A standard 10-gallon is about 20 inches long. Buy a bar with brackets that fit that length (roughly 18–24 inch class), not a reef fixture meant for a deep SPS tank.
What size LED for a 20-gallon tank?+
A 20-gallon long is about 30 inches; a 20 high is closer to 24. Match the fixture's adjustable brackets to the glass length. A 24–30 inch class bar is the usual 20-long pick.
Do I need a timer if the light has one built in?+
No. Use the built-in schedule. An outlet timer is for kit hoods and simple bars that only have an on/off switch, so the light does not sit on for 14 hours because someone forgot.