Mary Fisher wrote:

Says it all, really.

The butt started with coo muck and rainwater from the greenhouse roof drains
into it. It's not covered but has wire mesh over to stop birds drowning in
it. Another butt on the other side is covered.

I've had to use stored water from both to keep the greenhouse plants watered
this last couple of weeks, today I saw that the water in the uncovered one
was green.

I used it and am happy to continue using it (not that it will last much
longer without rain) but wondered if the Wise Ones hereabouts could warn me
if there are any potential problems.

Mary
--
Not in my name: http://www.stopwar.org.uk/

How about putting some barley straw in it? This seems to contain a
natural algicide and is recommended for controling algae in ponds. I
have tried it for this and it seems quite effective.
--
Larry Stoter