i Know it may be a hassle to move a lage plant ,but in nature the
minerals in the water are flushed through to the groundwater but
in a pot most of the water evaporates leaving the minerals and salts.
either take the plant out and let the hose run and rinse the soil
make sure the drain hole is clear of roots and the water is
flowing through the soil or put it in the shower and shower the
whole thing for 45 min or more but remember your rinsing the salt
out of the soil and there probly a lot there