as I understand it there are 2 important Ph measurements to adjust for, the mash Ph would be adjusted after the grains have absorbed the mash water and the temperature has settled out unless, if you have really really messed up water and the mash Ph is so high or low as to denature the enzymes then you would have to add salts before adding the grain (this usually doesnt work well because the salts don't dissolve well in plain water), and second is the Ph of your wort run off from the lautertun. I think the Ph is supposed to be between 5.2 and 5.4.
there are a few ways to deal with this, if your water is fairly normal you could use something like "5.2 Mash Stabilizer" it works well for most people but if your water is very hard or soft you might have to adjust things manually.
the second way is to add salts as needed to keep the mash and runoff Ph in the desired range, the third way is to try and duplicate the water of someplace appropriate for the style of beer.
for the third option you need a water report for you area so you know what your starting with then you need a selection of water salts (stuff like: Gypsum, Epsom salt, calcium chloride, sodium chloride, calcium carbonate, sodium bicarbonate, you can also use acids like lactic, phosphoric, sulfuric... anything food grade) I usually measure out two quantities of salts one for the mash water and one for the sparge water. ProMash software makes it easy to figure out how much of each of these salts are needed to duplicate a water style.
you can also stick to brewing the styles of beer appropriate for the water you have naturally or use malts that will lower the Ph to the desired level (Dark malts lower the Ph, I think I've also seen lactic acid malts that wont add a lot of color but will help lower the Ph).
both chlorine and chloramine can be a problem too chlorine can be removed by boiling but chloramine which isnt very common so not a huge concern needs to be filtered or chemically removed. campden (a pasteurizing / stabilizing agent for wines and meads) should take care of both it comes in two forms, sodium meta-bisulfite and potasium meta-bisulfite. you want the later as it doesnt add excess sodium to the beer.
There are a lot of good resources from people who know a hell of a lot more than I do, for example:
http://www.howtobrew.com/section3/chapter15.html
I hope I got all of this right, if I left anything out or got anything wrong Im sure someone more knowledgeable will correct me.