There is no "correct" answer to this question.
California only has a requirement of "reasonableness" in this area.
Much depends on the terms of your agreement and apparently the contract is silent on the actual charge. If a rent increase of less than 10% is given the landlord must give you a 30 day written notice or a 60 day written notice for increases of 10% or more.
You may live in a locality with a rent control ordinance and that may control whether any increase in rent is allowed or the amount that can be asked legally.
Consult a landlord/tenant attorney in your area.