When I'm not running the waterfall in my Koi pond, the rocks are bleached white. Why is that?

Question

I run the waterfall once a day for a couple hours. I live in Texas so during the day its about 90 degrees out. The Koi pond is made of rocks and mortar and I do have some string algae.

Answer 1

When the waterfall is running then algae will grow on the rocks. When you turn off the waterfall it dries out and bleaches in the sun. You will often see the same effect in a river as the water level falls over summer.

Ian

Answer 2

it could be the calcium deposits like in the aquarium tank.

kOi keeper & goldfish keeper

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