If it's a 5 stage then it should be a RODI
not just a RO
membranes have rejection rates of 90% - 98%, so your tap water at 130 would be at 13 - 3. Being at 7 means you are getting about 95%.
cartridge is what will take that down to ZERO.
It seems to me that the filter is working fine, but either you don't have a DI
cartridge, the DI
resin needs to be replaced, or you need to run it for another hour or two till it gets down.
But to answer your original question. A tds
of 7 is fine for filling a tank, and is Soooo much better than 130 tds
from the tap.