Flic Film Phenatol Green is a neutral tone paper developer designed for low environmental impact: its Phenidone-based formula is biodegradable and not-the-worst, though you should still take the usual precautions for mixing and disposal. This powder-based developer makes 4L of stock solution, which is normally mixed 1:3 with water, but can be mixed anywhere between 1:1 (for high contrast) to 1:4 (for low contrast.)