The Science
UV spectrum in natural sunlight triggers pigment cells to produce more color.
Different wavelengths target different colors — red intensifies most with afternoon sun.
Safe Exposure
Indirect filtered sunlight through a window for 2-3 hours per day.
Never direct unfiltered sun — causes algae bloom and temperature spikes.
Algae Management
Some algae is inevitable with sunlight. Accept minor green algae on glass.
Add fast-growing plants, reduce feeding slightly, or introduce a pleco.
Temperature Control
Sunlight heats water fast. Monitor daily — may need to reduce heater setting during sunny hours.
In hot climates, use a fan blowing across water surface for cooling evaporation.