Theoretically, galvanized iron pipes are suitable for all air conditioning and ventilation systems.

If the pool is wet and rusts, you can buy a thicker galvanized iron sheet. Brush anti-rust paint at the elbow of the air duct.

Composite air ducts are also acceptable, but only XPS extruded boards can be used. The disadvantage is that the fire protection can't reach the fire protection acceptance level B 1.

So it's up to you.