That link says a 4" pot is around one pint. So two 4" pots would be one quart, not one gallon.
Probably enough to treat a one-gallon pot would treat EIGHT 4" pots, guessing based on that link.
>> Example: Add 1oz. per 1gallon pot.
Therefor add 1/8 ounce per 4" pot.
1/8 fluid ounce = 3/4 teaspoon
1/8 ounce weight = 3.5 grams
For TWO 4" pots, combined, try 1 1/2 teaspoons or 7 grams.
