Symmetric aqueous organic redox flow batteries (RFBs) are potentially a cheap, durable and safe energy storage technology. Unlike normal asymmetric flow batteries, they are based on electrolytes that exist in at least three oxidation states and can undergo a minimum of two distinct redox processes. We compute the redox potentials of selected electrolytes intending to understand how the interaction between the redox units affects the potentials. We find that electronic interaction between redox units and intramolecular hydrogen bonding can both be exploited to tune the difference between the redox potentials, i.e. the theoretical voltage of the battery. The redox potentials can be further fine-tuned in either direction by adding substituents. Starting from these observations we formulate a set of rules which will help finding ideal candidates for symmetric RFBs.