If you are lowering both pH and alkalinity in the app, the results page will show two doses of acid.
The app gives two doses of acid when you are trying to reduce both pH and alkalinity. If you were only reducing one or the other, there would only be one dose. The other reason is because we now offer two types of acid, muriatic and sodium bisulfate (dry acid).
pH and Alkalinity
The LSI calculator's dosing function only knows the difference between the left and right sides (current chemistry and desired chemistry), and does not know you are trying to change both pH and alkalinity. So if you are trying to reduce both, only use the alkalinity dose, because the pH will be adjusted with that too.
We have tried to figure out a way to make it more intuitive, but it is more difficult than it sounds.
Two types of acid
Your question may also be about the two types of acid, muriatic and sodium bisulfate. This is no different than having calcium flakes and calcium prill/granular options for raising calcium hardness. The calculator is telling you to do either muriatic OR sodium bisulfate, not both.