If you haven't tested your water perameters do so... I've found 99% of "Illness" is directly related to water quality issues. General info such as tanks temp, water change regime ect is all really needed to best diagnose an issue. And no I have never seen this in any of my gar or heard this being "Normal" It appears to be the slaughing of the slime-coat or possibly a velvet infection ( not ick but can often appear similar to ick except is often accompanied by a "fuzzy" appearance)
DO NOT treat with meds until you can get a positive ID on a disease ( if that is the problem) Gar are extreamely sensitive to most common Meds used.
However I would increase my WC's, but until more info it's hard to say how much.. and how often would not only be most beneficial, But safe. fish use to regular large water changes won't be harmed by more frequent ones.. however a tank that isn't regularly use to large water changes may be more stressed then slowly building up to larger water changes. I have never had an instance where More water changes was detrimental to a fishes recovery, Only when to much is done on a system that is not use to it. more expensive yes.. but detrimental no.