I have one suggestion with your RO/DI set up. (I take no credit as I found the information elsewhere) Hopefully I can explain it so it makes sense, and this is all dependent on if you make RO water all the time or not. When the RO water sits in the filter system the TDS will rise until next use, this will then go directly in to the DI at a high TDS. This obviously floods the DI with high TDS water until the filter parts of the system flushes itself out (for lack of better terms) and depending on your DI's condition can raise the TDS output at the end product. So with that said, and after seeing it in my own system. I placed a 3 way "T" and a shut off valve in prior to the DI, this way I can divert the RO water from the DI until the TDS is ~2-3 after the membranes. It takes maybe 5 mins (starting from 190TDS the highest I have seen) to get to the 2-3 TDS depending on how long it has been since I made the last amount of water.
TLDR;
Basically I allow the RO water to go down the drain along with the waste water for a short period of time until my TDS from the RO water is ~2-3 TDS. I then direct it to the DI portion of the system and make my top off and water for water changes. In the end extending the life of my DI resin.
TLDR;
Basically I allow the RO water to go down the drain along with the waste water for a short period of time until my TDS from the RO water is ~2-3 TDS. I then direct it to the DI portion of the system and make my top off and water for water changes. In the end extending the life of my DI resin.