Remove limestone on the sides of the fiber pool

[FIFFI]

(Admin note: Poster is in Denmark & doesn't have access to US methods and chems!)

it a in ground pool from 1974. 38000liters / 10.000gallons with sand filter with 125kg sand in and a 1kw pump.
The pool havn't been used for 2 years before wee bought the house.
on the sides there is a lot of lime stone, its all white.
the pool is closed down for the winter now.

kasper