[kitch]

Hi I've 6 water butts in my allotment but only one keeps going green, I emptied it and. Scrubbed it then filled it back up but two weeks later it was green again.
Any ideas

[Aunt Sally]

It will only go green if light is getting in.

[JayG]

Agree - if you can see the water is green through the side of the butt it presumably is translucent and letting the light in, but if it's opaque and identical to the others it is a bit of a mystery. 

[mumofstig]

Add a touch of Citrox to the water to stop greening. It's perfectly safe for plants