They will eat Algae wafers and also other food tablets. If you've only just added them to the tank then they may not be eating because their getting used to their new tank.
They will also happily eat flake food that drops to bottom of the tank. Also, they will normally be OK just eating the Algae off the side of the tank (even, though it may get to a stage that you might not see it).
Hope this helps...
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