According to sources, the amount of KH2PO4 to add after a major water
change is 1/16-1/8 teaspoon. When using the Fleet Enema method, are
my calculations correct?

According to the package, each 188ml bottle contains 19g of MonoBasic
Sodium Phosphate and 7g of DiBasic Sodium Phosphate. That is 26g of
total available KH2PO4.

That works out to 2ml of solution roughly equivalent to 1/10th
teaspoon of pure KH2PO4 - right?

1/10 teaspoon in 75 gal - 1.18ppm
2ml of enema in 75 gal = 1.08ppm

Is this correct or am I an idiot?!

Thanks,
Greg