We all have issues with your TDS reading. You can not get zero TDS out of an RO. About the lowest is 1 ppm TDS. The max a good RO will give is about 98 %. Even if your tap water was 50 ppm TDS, that is still a TDS of 1 ppm.
As I said before, I also question you PO4 readings, as I never heard of RC having any real PO4. Here is an example of some salt tested in a research lab using ICP as just one example, although it is an old ICP study.
Take the blue number ppm PO4 = ( nmoles/l x 95 ) / 1,000
NSW = (.2 x 95) / 1,000 = 0.019 ppm .......( And is nmol not mmol, as mmol give 19 ppm PO4)
IO = (.05 x 95) / 1000 = 0.004 ppm PO4
RC = (.32 x 95) / 1000 = 0.03 ppm PO4
However, on reefs it is more on the order 0.004 - 0.009 ppm PO4
Our test kits or PO4 metes can not read as low as most of these numbers for salt mixes and when you throw in actual accuracy they are worse. Only down to 0.03 ppm PO4. And theri accuracy is +/- 0.04 ppm + +/- 4 % of reading.
is esv the best salt out there now?
There is really no such thing as "best", unless one has seen full blown data sheets. And having a so called "best" salt does not make or mean you will be more successful, it is a myth. A salt mix does not break or make a tank, the guy in the mirror does

There is no full assay sheet on ESV or any assay sheet. However, I know Bob, how he operates and feel it is a very good salt. I hope you know it is a multi-component salt, where you have to mix x amount of bag a, b and c. Based on raw data sheets the new SeaChem Labs salt, Aqua Vitro Reef Salt is the best.