Question
I have had a waterfall ornamental pond with goldfish in it since last August. We have had the regular green string algae but just this week I have noticed a brownish orange film on the rocks to the waterfall. It looks like rust from far away but when you feel it,it feels like a slimly covering over the rocks. How can I get rid of this? We are in mid-michigan.

Answer
It's probably a mix of brown and green algae with dirt and microorganisms. Think of it as the pond's skin.  It's probably nothing bad.  If you want to remove it, then physical removal for small areas is best.  If it includes brown algae, then that type of algae likes lower light levels.  Green algae likes stronger lighting. If algae is involved, then adding plants to the waterfall like watercress will shade out and compete with the algae.  I get a similar coating on parts of my pond that has dirt mixed with algae and micro-life.  It sometimes flakes off.  Animals (in the waterfall, that would mean insects and snails) can help dislodge the stuff too.  My page on pond algae in general is at http://www.fishpondinfo.com/plants/algae2.htm
They keys for algae control are plants, low light, good filtration, good bacteria, barley straw, and more plants.  Good luck!

Robyn