Comment by westurner

From https://hps.org/publicinformation/ate/q12178/ :

> UV light, a form of energy, is defined as light having wavelengths between 100 nanometers (nm, 1 billionth of a meter in length) and 400 nm. [...]

> Most acrylic plastics will allow light of wavelength greater than 375 nm to pass through the material, but they will not allow UV-C wavelengths (100–290 nm) to pass through.

In terms of photonic permittivity, Glass is better for cold frames and the like, because acrylic filters out UV light.

Also, Hydrogen peroxide (H2O2) is an algaecide.

/? hydrogen peroxide algaecide https://www.google.com/search?q=hydrogen+peroxide+algaecide