One site recommends using a little bleach,not much,in the water or possibly try some hydrogen peroxide. Brady

We just scrub our fountains with a hand brush & spray hard with the hose. Over winter I bought a fountain cleaning kit at Lowe's, but since we've not had algae yet we've not used anything out of it.

Whatever you use make sure it's okay for birds if you have them frequent your fountain. We have many birds use them: songbirds, hummingbirds & in that last droughty period crows. One fountain is low enough that our dog drinks out of it.

I've not yet used Mrs. Stewart's bluing, but you can read more about it on their website because they say no complaints from it being used around animals since 1883.

To prevent growth check your pump & tubing. When the fountain tubing is clogged with fir needles & less water volume circulates we have had algae growth in the past.

Here is a link that might be useful: blue iron powder, biocide, ph balancer