A mirror shows food coloring disappearing under this skimmer.
Two-part pool putty is used for a long term repair of this type leak.
Use your stiff brush to remove any loose plaster and algae. Mix equal parts of putty and apply. Smooth putty over the leak site.
One of the oddities of putty is that it initially softens in water, becoming almost 'gummy'. Check your work in ten minutes to make sure it hasn't been swept away.
Clean-up is with water and a pumice fortified soap.
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