I don't see anywhere on that page that recommends adding acid of any kind to your starter, but then I didn't read the whole page. I did a search for "lactic", "acid" and "ph" and only saw that it says your pH of your starter should be 5 or something. You aren't correcting your water to 5 are you?
I see he says this, MY bolding here:
The pH of a starter needs to be around 5 pH, but if you can’t test it, don’t worry. Typical wort ranges between 4 to 6 pH, so use a high quality DME and it will be OK.
I don't think it's necessary to add acid to your starter. If your pH is too high, I'd cut it with distilled water first then add back 1/4 tsp of yeast nutrient for the yeast (that Wyeast nutrient or equivalent, not DAP). I don't think I've ever heard of anyone using acid of any kind in a starter. Acid is rarely used at all in the home brewery. Most people add it to their sparge water to keep that pH from straying too high and extracting too many tannins during runoff.
If anyone else is using acid in their starters, by all means please chime in.