Nelly wrote:

As well as water quality, dosage might depend on what brand you use.
Some products labeled "TSP" can be less than half that. Savogran's is
like 80%, might be ok except I don't know the safety the other stuff
in it. Here's one place to get the pure stuff:
http://www.cqconcepts.com/chem_tsp.php

Absolutely! I've got a spray bottle on my desk labeled "TSP - Ready To Use"
and, in fine print below: "Phosphate-free"!