Aquarium Lights in Fall: How Many Hours, and What Riparium Plants Above the Water Need

When the days get shorter, a lot of people leave the tank light on longer to make up for the dark living room. Then the algae shows up. Here's how to set the lights through fall and winter, and what's different about the plants growing out of the water in a riparium.

How many hours?

For most planted freshwater tanks, the light should be on about 6 to 9 hours a day:

• New tanks, or tanks fighting algae: start around 5 to 6 hours.
• Stable, low-tech planted tanks: 7 to 8 hours.
• Heavily planted tanks with strong lights and fertilizer: 8 to 9 hours.

More than about 10 to 12 hours doesn't grow plants much faster, but it does grow algae. Fish don't need the light at all, beyond seeing their food. They need a regular day and night.

Use a timer

The best upgrade you can make to any tank is a $10 outlet timer, or the built-in timer many LED lights have now. It gives the fish and plants the same day every day, and it stops the "forgot to turn it off" nights that cause algae blooms.

A tip: split the light into two blocks with a break in the middle (say, 4 hours in the morning and 4 in the evening) if you want to see the tank before and after work. Some keepers find this helps with algae; at minimum, it doesn't hurt.

What changes in fall

• Window light drops. A tank near a window that got a couple of hours of sun all summer suddenly gets almost none. If it was growing well in summer, you may need to add an hour of tank light.
• Or window light changes angle. The low fall sun can shine into a tank that never got direct light before. Watch for a new green film on the glass on one side.
• Room light goes on earlier. If the living room lights are on until midnight, the tank's "night" is shorter. Fish do better with a real dark period.
• Room temperature drops. That's a heater issue, not a light one, but they show up together. See our cold-water heater guide.

Lighting the plants above the water

A riparium has plants with roots in the water and leaves in the air, like pothos, peace lily, anubias, umbrella palm and many others. They need light too, and the light above a regular aquarium often doesn't reach them well.

• Hang the light higher, or use a pendant light, so it covers the leaves above the waterline and the water below.
• Emersed plants usually want more light than the underwater plants. A strong LED or a clip-on grow light aimed at the top of the riparium works well.
• Keep the light off the glass lid, or clean the lid often. Mineral spots and condensation block more light than you'd think.
• Watch for stretching. Plants that stretch, lean toward a window, or lose their lower leaves need more light.
• Watch for burning. Pale, yellowed or crispy leaves right under a strong light need it raised or dimmed.

Many of the best riparium plants are common houseplants that do fine in average indoor light. Our riparium plants guide lists the easy ones. Plants that grow on rock, like java fern and anubias, are happy in low light both above and below the water.

Moonlights

Blue "moonlight" settings are fine for watching nocturnal fish like bristlenose plecos and loaches in the evening. Just don't leave them on all night every night.

Sources (1)

2Hr Aquarist: Planted Tank Light Hours

Photo: Amaterske akvarium by User Aleš Tošovský, Public domain.

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