Direct answerBoth filter types can work when sized correctly.
What to check first
Sand filters need a backwash waste route.
The existing pool, property access and equipment condition can change the answer. Record what is happening before adjustments are made.
What affects the work
Cartridge filters need space for element removal.
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.