Direct answerGrout closes tile joints but is not the main waterproof layer.
What to check first
Remove enough weak grout before replacement.
The existing pool, property access and equipment condition can change the answer. Record what is happening before adjustments are made.
What affects the work
Allow the product to cure before filling.
A clear scope should separate inspection, repair and optional improvement work. This makes quotations easier to compare.
When a site visit is useful
A site visit is needed when the answer depends on pipework, water loss, structural movement or the exact equipment installed. Photos can narrow the likely cause but cannot confirm a concealed fault.