[russell]

  Doing a RIS and planning on putting in the steeping the dark grains at sparge. If I take a PH reading at like 15 minutes from the start of the mesh, the PH will be different from the end of the mash because I add dark grains at the end of he mash which bring down the PH.  If I add 2 ml of lactic acid at 15 minutes it may not be enough. How do you guys do this? Do you check the PH at preboil and adjust it from there?

[denny]

The dark grains will pull the pH down and lactic acid will pull the pH down evenmore.  I wouldn't use it.  Plus if you add them at the end of the mash the pH won't matter much.

[mabrungard]

While delaying the introduction of roast grains to the end of a mash can help avoid the problems in mashing at an overly low pH. But it doesn't avoid the problem of ending up with a kettle wort pH that may be lower than desirable for beer flavor and perception. Sometimes, there is no substitute for proper mash and kettle pH and this technique is useless under that condition.

[HopDen]

I don't know what your water profile is before any treatments. Do you treat your own water? RO or distilled and then add minerals back in? Could you make the water with a higher carbonate, bicarbonate level to offset the effects of the darker grains?

[russell]

 not sure how this answers the question of how to lower the PH after sparge other than knowing the Pre boil PH but here is the water profile.
my water profile: 
Calcium- 42ppm
Magnesium-8.4 pm
Sodium- 43 ppm
Sulfate-71 ppm
Chloride-41 ppm
Bicarbonate- 110 ppm