Euphotona is an advanced yet intuitive scientific calculator designed for marine optics and environmental remote-sensing studies. It estimates how sunlight penetrates the ocean by computing the euphotic depth and optical attenuation coefficient from measurable water parameters such as chlorophyll concentration, turbidity, wavelength, and solar zenith angle. Using an educational empirical model that blends biological and optical effects, the app helps visualize how clarity, productivity, and light absorption vary across different water types. With a clean ocean-themed interface, real-time results, copy and share options, and clear validation feedback, Euphotona serves as a compact digital assistant for oceanographers, climate researchers, and students studying underwater light fields and marine ecosystems.