[MattyAHA]

 i dont know much about acids or water chemistry, i normally would use brun water but my computer is jacked up and freezes everytime i try to open the spreadsheet, im starting with distilled water, mash volume is 3.75 gallons adding 1 tsp of gypsum and .5 tsp of calcium chloride and the est mash ph is 5.7 so in order to bring it down to 5.4 i need 36.5 ml PA according to this online brewers friend calculator, idk but that seems like an excessive amount of acid, the question is ,is it an excessive amount?

[brewsumore]

very excessive - there's an error there.

[MattyAHA]

yeah i figured it was a error, im gonna just toss 2.5% acidulated malt in the mash and if the ph is not low enough just add some PA 1ml at a time until its where i want it to be, cheers

[Buddylee000]

I think it could be possible depending on the concentration. I know the homebrew store I go to has concentrations in bottles as low as 10 or 15%.

[dmtaylor]

Could be possible if it's a very weak 5% solution.  Otherwise unlikely.

[Robert]

IME that Brewers Friend calculator gives some pretty wack acid amounts.

EDIT  I just did some quick figuring.  From long experience, I'll say that with all pale malt,  RO water, and about 100ppm Ca which I assume you'll get from your salts (since you gave teaspoons instead of grams,  actual dosage is a shot in the dark,) you won't need any acid at all to get a pH in the correct range.   Assuming a 10#, all Pilsner malt grain bill, Bru'n Water confirms pH estimate of 5.51.  Further, Bru'n Water calculates that to bring this down to 5.4 with 10% phosphoric acid requires 2 mL/gallon.  Lots of assumptions,  but hope this helps.

[brewsumore]

Could be possible if it's a very weak 5% solution.  Otherwise unlikely.

I didn't do the math, but in my initial response I admit I didn't allow for the possibility of a very weak concentration of phos acid.  Personally, I use 85% phos acid.  It's much more economically beneficial for my brewing schedule.