Quick answer: bettas like light.
They need it to know when to wake up, and they need darkness to rest. What they hate is bright, glaring light, and what stresses them most is the wrong light at the wrong time.
That last part is where most guides go quiet. They tell you to run a light for “6 to 10 hours” and call it done. But if your betta hides behind the filter, paces the glass, or flares at the tank walls when the light is on, the problem isn’t how many hours you’re running it. It’s what you’re running, and how bright.
Here’s what actually matters, in the order your fish cares about it.
Do Betta Fish Like Light or Dark?
Both, on a schedule. That’s not a hedge; it’s how the species evolved.
Wild bettas live in the rice paddies, swamps, and roadside ditches of central Thailand. Those waters are shallow, still, and often shaded by floating plants, tall reeds, and overhanging vegetation. Sunlight reaches the fish filtered and dappled, not blasting. Seriously Fish, the standard reference for freshwater species, describes the natural setup as “well-planted, shady” with “plenty of surface cover.”
So a betta’s brain expects bright day, dark night, and a lot of dim, broken shade in between. Light tells him the day started. Darkness tells him it’s safe to rest. Strip out either one and he starts running on a schedule that doesn’t exist in nature.
One keeper on bettafish.com put it as plainly as anyone has: “Betta are shade-loving fish. They do not do well in bright light.”
How Many Hours of Light Does a Betta Need?
8 to 10 hours a day is a safe default.
- 6 hours or less cuts algae growth noticeably. It’s the number you’ll see from keepers fighting green water.
- 8 hours is the ceiling most long-time keepers quote. Regulars on FishLore and AquariaCentral both say the same thing: more than 8 hours and the fish doesn’t get enough rest.
- 10 hours is the high end, fine if the tank is heavily planted and the light is gentle.
- 14 to 16 hours gets thrown around by one major betta retailer. That number is an outlier, and it’s worth knowing why: they sell lights and plants, and long photoperiods make plants grow. Nothing about a betta’s biology needs 16 hours of light, and most keepers treat that advice as the affiliate page it comes from.
A timer makes this set-and-forget. A schedule that works:
- 9am to 5pm: daylight
- 5pm onward: lights off
- overnight: total darkness
Do Bettas Need Light at Night?
No. Bettas need it dark at night, and total darkness is fine.
Bettas do sleep, just not the way mammals do. They doze in short bouts, often hovering near the surface (they still need air) or tucked against a leaf, and they need the lights-out period to actually do it.
Leaving the tank light on 24/7 does three things: the fish never gets proper rest, stress climbs, and algae takes over because there’s no dark period to slow it down.
One experienced keeper on Quora summed up the whole argument in a sentence: the tank light should be off for most of the 24-hour day. If the room the tank sits in gets decent natural light, the fish may not need the aquarium light on at all.
Do Betta Fish Like Blue Light? No, and Here’s Why
The “moonlight” or blue night mode on LED fixtures is the most common mistake in this subject, and it’s the reason so many bettas act up after dark.
The evidence is all over the forums. On fishforums.net there’s a thread literally titled “Blue Light Makes Betta Evil”: a keeper’s betta was fine all day under white light, then flared and chased tankmates the moment the blue light came on. On AquariaCentral, the same story: peaceful all day, aggressive toward neon tetras at night once the blue LED was switched on.
Three things are going on, and they can stack:
- Bright colors read as rivals. The usual keeper explanation: bright colors read as rivals, since in the wild bright color usually means another male. A blue wash can register the same way as a flaring intruder, especially for a fish that’s already keyed up. It’s also why some bettas flare at bright ornaments.
- Reflections. Tank light on plus room light off turns the glass into a mirror. The betta sees his own reflection, reads it as a rival, and spends the night flaring at the wall. Keepers report this exact behavior with blue lights and with reading lamps bouncing off the tank.
- Blue light doesn’t give rest, and it feeds algae. Light is light to a fish. Blue mode isn’t a lullaby; it’s still a light source keeping the fish awake. And as regulars on the Aquarium Co-Op forum put it, algae has a lower light threshold than most plants, which is why a tank left in “moonlight” mode can grow green fuzz the plants never outcompete.
There’s one legitimate exception: breeders sometimes run a dim light in a corner of a fry tank to stop adults from eating eggs and young at night. That’s low intensity, one spot, not the full blue setting. Unless you’re breeding bettas, skip the blue mode entirely.
One observation worth knowing: some keepers report that full-spectrum lights with a red channel seem to calm bettas and grow plants better. That’s forum observation, not settled science, but if you’re shopping for a light anyway, a dimmable full-spectrum fixture gives you the most room to adjust.
Why Does My Betta Glass-Surf When the Light Is On?
Glass surfing is the betta pacing back and forth along the glass, and r/bettafish has a whole shelf of threads about it: “Betta glass surfs when light is on,” “New Betta constantly glass surfing, changing lights.”
If yours does this when the light is on, work down this list:
- Too bright. The light is stronger than the fish can handle. See the fixes below.
- No shaded spot. A betta in an open, bright tank has nowhere to go. Shade changes everything.
- Reflection. Same mirror problem as above. Check whether the room is dark while the tank light is on.
- New tank. A betta that just moved from a pet store cup into a bright new tank is stressed by everything, light included. Keep the light off or dim for the first few days while he settles in.
Glass surfing isn’t the only stress sign tied to light. Constant hiding, washed-out color, clamped fins, and a fish that stops eating all point the same direction when they show up under the lights.
How to Fix a Tank That’s Too Bright
Shading beats dimming. You don’t have to buy a fancier light; you have to give the fish somewhere the light doesn’t reach.
- Floating plants. A mat of Salvinia or similar floaters turns a blazing tank into a dappled one in a couple of weeks. Keepers use it as a shade canopy on purpose, and it doubles as cover the betta genuinely uses.
- Tall stem plants and broad leaves. Jungle val, Cryptocoryne, Amazon sword. Seriously Fish’s own betta setup calls for exactly this: “well-planted, shady.”
- A cave or hide. Half a clay pot, a betta log, anything dark. One experienced keeper’s position is that as long as the fish has cover, normal lighting is fine, and for a lot of bettas that’s true. Try cover before you spend money on a dimmer.
- DIY dimming. Kit lights often can’t be dimmed, and keepers have worked around it: USB LED strips with three brightness settings placed around the tank, or a desk lamp with selectable modes instead of the tank light entirely.
Two things to never do: put the tank in direct sunlight (it overheats the water and grows algae like nothing else) and run a 100% intensity fixture on a small tank. Most kit lights are brighter than a betta needs.
Do You Even Need a Tank Light?
Depends on the room, not the fish.
If the tank sits in a room with good natural light during the day, the betta may never need the aquarium light switched on. Keepers have moved betta tanks to the sunniest room in the house and stopped using tank lights entirely, with the fish doing fine.
If you keep live plants, that changes. Aquarium plants need more light than a betta does, and a planted tank without a proper light will slowly starve the plants. In that case run the light, keep it gentle, and stick to the 8 to 10 hour schedule.
