Anytime someone has a "will this hurt me" question related to chemicals, the first place to check is the Toxicological Information section of that chemical's MSDS (Material Data Safety Sheet) - a Google search should locate one.
In this case the MSDS does not specifiy any human toxicological information, but it does list this: Toxicity to Animals: Acute oral toxicity (LD50): 3800 mg/kg [Mouse]. BTW, LD50 refers to a Lethal Dose for at least 50% of a test population.
Even though we are not mice, will adding 3 Tbls of Sobistat-K to 5 gallons of liquid exceed the 3,800 ppm LD50? The short answer is no. To achieve 3,800 ppm one would have to add 7.2 Tbls and you only added 3.
One variable not described was what type of tablespoon measurement - heaping, rounded, level? While this might seem like splitting hairs, it is important as Sorbistat-K has a low density, and volume measurements (like a Tbls) are not as accurate as measurements by weight, which is the foundation of a ppm calculation.
Even considering that factor, the error margin is over 50% to reach the LD50 and you should be safe...
