green algae on drinker

I have a metal drinker for my girls that I freshen up either daily or every other day.  I have used poultry shield to clean it then rinsed it thoroughly but it still seems to be growing green algae after a day.  Can anyone out there advise me how to get rid of the algae.  I'm sure it can't be good for the girls.
Many thanks

It wouldn't grow green algae within a day I'm sure.

Give it a good clean with a washing up brush.

I scrub mine out every week with normal fairy liquid. You just have to do it as soon as you see a tinge of green.
Part of the routine....

An old toothbrush is really handy for awkward little bits. The groove which allows the water into the drinking area is always worst on mine.

I have the same problem even if cleaned out religiously, daily. Mine is hung in the shade. It is a problem that is bad in warm weather I do not get the problem in the winter. The horses troughs are the same.