Actually sodium chlorite powder is only 80% pure. The solutions are made up by weight. For example, if you take 25 grams of sodium chlorite powder and add it to 400 grams of water you will end up with a 6.25% solution by weight, but it will actually only have 5% sodium chlorite in it.
In the same way the 28%, by weight, solution is actually a 22.4% sodium chlorite solution.
When using citric acid to activate, the proper ration is 10:1 when using sodium chlorite and citric acid powder, 5:1 when using 50% citric acid , and 1:1 when using 10% citric acid. These ratios have been extensively tested and found to be the most effective way to activate sodium chlorite.
Your stoichiometric calculations are close, but you will have a more effective solution if you follow the proven ratios for activation. With billions of pounds of food at risk of spoiling if the ratio is not effective, I would suggest going with what has been proven to be the most effective.