Brita is a carbon type filter... It pulls out heavy metals and usually lowers Totally dissolved solids by 25%... If your starting at 300 TDS it will end up around 250 TDS... Our bodies have to have trace elements in the water we drink... Brita filters will never get the TDS of water to 0 TDS. Your goal should be 0 TDS which is only hydrogen and oxygen molecules without all the extra trace elements the city puts in our water in order for it to be consumed. If high TDs water is used algae will consume any trace elements they can in order to grow, Phosphorus, nitrogen, potassium, iron, etc. If you use 0 TDS water there are no other elements in the water you are using for top off or mixing synthetic salt. Another benefit for using 0 TDS RO/DI water is the deionization that occurs allowing the ability to absorb vital trace elements that you dose in your system, such as magnesium, calcium, and alkalinity. Hope this helps and wasn't over the top. ;-)