An RODI unit will help to some degree but not specifically to reduce or eliminate any current issues you are having. Depending on the how your filter is setup, ie: the types of pre-filters, total number of stages, what kind of DI Resin used, even the inlet water PSI all ultimately determine the quality of product water you're able to produce. Most municipal tap water supplies have fairly high TDS levels, there could be ammonia, chlorine, chloramines, fluoride, phosphates, any number of different types of metals, organic compounds, arsenic, and even possible radioactive contaminants, etc. A RODI unit if setup correctly can remove up to 99.9% of the various contaminants found in source water. By removing all these contaminants prior to mixing in your salt, you will have better control of what goes into the system and thus can make it easier to fix issues water parameter stability and to some degree nutrient levels.
If you're having issues with nuisance algae like hair algae, you would need to either treat the system with fluconazole at
@Tenny suggested, also look into how this became an issue to begin with. Also look into possible livestock options that will naturally control it as well. Getting the phosphates down to a manageable level is also important as is adding macro-algae that will out compete the nuisance algae for nutrients ultimately preventing them from getting a foot-hold in your tank.
So, yes having an RODI helps, but don't expect miracles with having it now. More accurately, a RODI is an extremely valuable tool for keeping a successful reef tank.
