the water in 1 of the water butts has developed a coveing of green slime, which now has 'bubbles' in some areas as well.
Is it ok to use for watering plants or should I dump all the water and clean out the butt?
if it were me I`d empty it as its in full sun.. clean it & put back..
I would empty it and clean the butt thoroughly and if you can move it to a cool and shady part of the garden. If yourwater butt collects grey water ie from your household taps then I recommend using a water butt treatment to keep it scum free, HOZELOCK WATER TREATMENT is good.
Hope this helps