Rocks forming black something


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I did a thorough cleaning of my pond and waterfall 10 days ago. Removed the fish to a holding tank and removed all the river rock after power washing everything to remove four inches of muck and reposition the rocks. The pond is in the full blazing Arizona sun for eight hours a day. Before I did the cleaning I had lots of string algae on the waterfall rocks and in the pond. It kept the water clear and the fish fed. I didn't have plants because of raccoons. I added some small plants after cleaning hoping they will grow and keep the water clear and the algae level down (I cover the pond at night to keep the raccoons from getting the fish and tearing up the plants). Now the water is a very pale green tint and the tan waterfall rocks turned black with a light coating of green algae. I brushed off the algae but the black stayed. I probably needed to keep more algae on the rocks, but the guy that did the power washing forgot. Over the years I haven't tested the pond water or used additives - it stays clear and I haven't had any goldfish die. I did find quite a few more babies than I thought I had from the four one inch fish I put in the pond last summer (they are now four inches). Any idea what the black is and if it will go away as the pond settles in? Any other tips on pond cleaning for the future?
 
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JRS

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Could be algae in the pores of rock. I have also seen dark areas on parts of rocks that were touching, possibly some anaerobic discoloration.
 
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Sorry to say this, but the only "cleaning" you should have done was to slowly net out the muck from the bottom or use some kind of pond vacuum.

Totally cleaning and power washing is a big no-no. You killed off all the natural beneficial bacteria and biofilm.
Your pond water will most definitely turn green now. We call it new pond syndrome.

Since all the protective good stuff is gone, nature will now provide the protection needed in the form of algae. The result is green water. It will take time for your pond to return to it's natural balance. Maybe a month but most likely longer.

You need to add competition against the algae which is done by adding lots of plants.

Your filtration needs to be adequate also.
 

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