I used to get rock work from a landscape yard on the WI/IL border, where they would weigh my truck on the way in, and on the way out.
I would take an eyedropper and small bottle of vinegar in and put few drops on the rocks to see if they sizzled.
These days I collect plants from Lake Gatun Panama, or other local waterways.
Some plants work, some don't.
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The Hygrophilla above has done well
The Salvinia and water lettuce below, started as 1 or 2 plants each
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The Mangrove pods were also found washed up on the Pacific shore.
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Logs washed up are also used, as are terrestrial tropical plants hung on the surface of the tank.
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