I'm no expert, but I’ve had a SWG for a little over five years now, so I may be able to help.... While I really believe you should pay attention to the manual for your unit regarding dry acid, you said you dissolved it first and poured it in away from the skimmer--I can't see why this should present a problem for the unit. I really think the ‘low salt’ indicator and the addition of the acid may have been a coincidence.

While I don’t have the same unit as you do, my low salt indicator will shows up (off and on) when it needs more salt. This is usually most apparent when the pool is stirred up--by swimmers, or during the addition of chemicals. It rarely stays 'on' consistently, but I always test it whenever I see it go off and then back on--it usually needs more salt (or all of the salt I've added has not yet dissolved). Whenever it gets below 3,500 ppm, off it goes. Since you said you believe yours is around 3,300 ppm, I'd suggest adding more salt to ensure the level stays above 3,500 ppm. For my unit, I’ve found that 3,500-4,000ppm is ideal. It gives me a buffer; and I've been told that you don't need to worry about equipment corrosion from excessive salt, unless it gets above 6,000 ppm.

Again, I’m no expert, but according what I’ve read, it takes 50 lb. salt per 2,000 gal. of water to reach 4,000 ppm in a newly filled pool. In future years, you will need to test before adding any salt, as the salt is only diminished by water removal (backwashing, splash out, draining). Hope this helps…