Most manufacturers specify that "pickling" your R/O unit is good for up to a year.
I believe you are a new owner, so someone else pickled the unit, 4 years ago. Proper pickling is essential for even a one-year storage
I certainly would NOT TRUST in either the (the other guy's) process nor the 4-year interval.
, after long-term storage
, requires a four-step process:
2. Alkaline cleaner to remove/neutralize biological materials. Best if used /w HOT water
(120 Deg. F)
3. Acid cleaner to remove mineral scale.
4. Final purging & product-water quality test.
Specific instructions should be available from the manufacturer (which I recommend); but I could offer a "little" more advice if you described your system.
Take care - it's important!