Post TDS readings

[spikehs]

I was just wondering what my TDS reading should be at post RO/DI. I have the aquasafe 5 stage RODI. My starting tapwater is about 190... I have had it running for about 30 mins, and it is currently at 28... I figure it should be lower no? Giving that I am just filling up my tank for the first time, i dont want to start filling it up until the TDS is at an acceptable level, would in the 20's be considered high for post RODI? thanks.. btw all the filters are brand new. Thanks!!!