Have you tested for dissolved O2? 128 TDS is a pretty large jump - sounds like something got into the container.
Off-gassing shouldn't effect TDS (as dissolved gases are not dissolved solids) - Just like "Ihavecrabs" mentioned, you most likely culprits are
1) Something got into the tank, maybe was already even in the tank (like a small chunk of salt) - and dissolved into the new water. Gasses will not show as a TDS on your TDS meter.
2) The tank is 'leaching' into the water. I have had 100's of friends/customers use "non food grade safe" plastic on RO/DI water, and what starts off at 0ppm, can be over 50ppm within a few hours. You're not quite at zero - but 3 ppm is pretty clean water and I would expect the waters behavior to be somewhat aggressive as Zero-TDS water is.
Clean a glass with RO water, rinse with RO water - and then try storing some fresh RO water in that now clean glass - you should find that the TDS does NOT change over any period of time (unless something gets into the glass) Additional off-gassing (like you mention in a 3rd container) wont address this issue.
Let us know what you find!! Happy 2018!! :)