Considering CH3COOH, K2SO4, KOH, NH3, Ca(OH)2 and C2H5OH, why do some affect a concentration of Cr2O4-2 or Cr2O7-2 and others do not?

It depends if they react of not.

Write the equations for both the dissociation of the different chromates.

(note, the first one is CrO4 and not Cr2O4)

I will take the dichromate VI for I only have it's equation.

Cr_2O_7^{2-} + 14H^+ + 6e^- \rightleftharpoons 2Cr^{3+} + 7H_2O

Removing the Cr^3+ ions or the water will tend to shift the equilibrium to the right (according to Le Chatelier's Principle) and hence, the concentration of the dichromate VI will decrease.

In the other way, removing the H^+ ions will shift the equilibrium to the right, hence increasing the concentration of the dichromate VI ions.