Guide 38 — Setup Guide

Lighting Basics for Planted Snail & Shrimp Tanks

Lighting is the input that drives almost everything else in a planted tank, including the algae covered in our previous guide. This one covers intensity, photoperiod and how to strike a balance that grows plants without feeding algae.

Intensity: What PAR Actually Means

PAR (Photosynthetically Active Radiation) measures the amount of usable light actually reaching a given point in the tank — a more meaningful figure than a light's wattage or lumen rating alone, since those don't account for spectrum, distance from the water surface, or how much is absorbed before it reaches plants near the substrate. Low-tech, low-demand planted tanks generally do well with modest PAR — enough to support easy, undemanding plant species without pushing growth so hard that nutrient uptake struggles to keep pace, which is one of the more common triggers behind the algae types covered in our Reading Algae guide.

You don't need a PAR meter to get this broadly right. As a starting principle, more demanding, colourful or fast-growing plant species need noticeably more light than hardy, slow-growing species like many mosses, ferns and Anubias — matching your lighting to the plants you're actually keeping, rather than buying the most powerful light available, avoids creating more intensity than your plant mass and nutrient dosing can use.

Photoperiod

Photoperiod — how many hours a day the light is on — is usually a more useful lever than intensity for a beginner to adjust, because it's simple to control and directly affects algae pressure. A common, well-tested starting point for a low-tech planted tank is around 6-8 hours a day on a consistent timer, rather than leaving lights on for convenience across a longer stretch of the day.

Balancing Light Against Nutrients

Light drives plant growth, but plants can only use that light if the nutrients and, in higher-tech setups, CO2 to support it are also available. Strong light with limited nutrient availability is one of the most reliable ways to trigger algae, because the light energy is present but the plants can't fully use it — leaving the surplus available for algae to exploit instead. This is why simply turning up the light rarely improves a struggling low-tech planted tank on its own, and why a tank that's genuinely balanced tends to need less light than an unbalanced one to look the same.

For low-tech tanks without pressurised CO2, keeping light moderate and matched to slower plant growth is generally more reliable than trying to push high light without the CO2 to support it — our CO2 guide covers where that line sits and the invertebrate-safety considerations involved if you do want to go down that route.

Lighting Considerations Specific to Snails and Shrimp

Beyond plant growth, lighting affects the livestock directly. Very bright, direct lighting with no shaded areas can leave shrimp and some snail species feeling exposed, reducing natural daytime activity as they seek cover instead. Floating plants, dense stem plants or simply positioning hardscape to create shaded pockets gives shrimp and snails somewhere to retreat during brighter hours while still allowing normal plant growth across the rest of the tank.

New arrivals in particular benefit from subdued lighting during the first acclimation period rather than being introduced under full brightness, which is worth bearing in mind alongside the acclimation steps in our general livestock guides.