"Please inform us of the quantity of solvent you require(d) each month."
I'm not sure if you're asking about the tense of the 'inform' (correct), 'is' (correct), or 'require' (possibly correct).
You can't say "those solvent". The use of "Inform us what is ..." is not good. Another option is "Please inform us what the quantity of solvent is that you require each month."
If the sentence is about the past use of solvent, then 'required' is correct, and you need 'was'.
Student or Learner