Thanks ....

OK, I think I've got it figured out . (I never was too good at math though ......
The recommended dosage was 20 mg/liter
30 gallons of water = 113.69 liters
20 mg/liter x 113.69 liters = 2273.8 milligrams needed
2273.8 mg = 2.2738 grams
2.2738g = 0.080205935 ounces
4 teaspoons = 1 ounce
4 teaspoons / 0.080205935 = 0.32082 teaspoons or 1/3 teaspoon

If that's the case, I overdid it, but it has seemed to help the larger one, so I'll do a 50% water change tomorrow to dilute the magnesium sulfate