It looks like the Dolomite Lime contains Calcium and Magnesium Carbonate, CaMg(CO3)2, thus could potentially through off the balance of mineral elements in your nutrient solution. I'm not a chemist so I don't know how the Carbonate part of the Calcium and Magnesium Carbonate part factors in, or what is processed in, or out (if any) of Dolomite Lime for the agricultural product. However I know that General Hydroponics makes a product called CaMg+, though GH doesn't list ingredient, or say how the product is manufactured, or what it's derived from etc.. Just that it's a Calcium and Magnesium supplement.

Also it appears that Dolomite Lime is intended for use in soil. I'm not clear on how much of it is readily water soluble, and/or how much of it actually needs to break down first (like in soil). I haven't used it for anything myself, I just looked it up to see what it was.

Here's something that I found that talks about using dolomite lime, as well as lime quality.
Soil Acidity & Liming

Speedfreakian;
Dolomite Lime is definitely a base and therefore will bring your ph up. However I've never heard of anyone using it in hydroponic applications. In all likelihood this is due to solubility or lockout issues. If it were a practical ingredient I think many hydro growers would be using it.
I have several questions;
When is your ph at 4-5?
I've never seen water that low.
After you add nutrients?
Although many mineral salts in nutrients are acidic, 4-5 still sounds quite low to me.
Does it drop down to 4-5 throughout the week?
If I'm not mistaken this could be caused by dead or dying root matter.
Is your reservoir large enough for the amount of plants?
My ph does drop between change outs, but not nearly that much or that fast.
If ph up is not available, try sodium bicarbonate (baking soda). It works for me.
Good Luck,
~Ken~