Since you don't say what size tank, it is hard for us to calculate, but...
An average 100-120 gal tank, will need "3.5" LBs of salt to get salinity high enough to make a dent on the ick.
And if you were wimpy with the salt before (using 1tsp per gal is like doing nothing),after adding the 3.5lbs will be like starting all over, and ick can take 3-5 weeks to eradicate, because each protozoa needs to complete its life cycle, and its progeny need to be exposed to and killed by the salt.
By adding too little salt at first, you allowed and progeny that survive to become slight salt tolerant. Don't wimp out.
You may be at a point of no return, because...
If you do wimp out, your fish will die anyway, so what's the point of being wimpy.
Below is link to a salinity calculator
Direct Salt Addition Calculator - Hamza's Reef