Farm1 wrote:
Huh? I know sod all about Chemistry but even I know Washing Soda is
sodium carbonate whereas salt is sodium chloride.

Sodium Carbonate (Na2CO3) is a salt. Sodium Chloride (NaCl) is table
salt, but there are many other salts.

Are all sodiums bad for soil or just in significant quantities or
what?

I would imagine that Sodium Carbonate would be just as harmful
as Sodium Chloride.

I attended a greywater workshop a couple of years ago with
Ross Mars, and he said that many washing detergents have
increased levels of salts to compensate for reduced phosphate
levels. He showed us a table showing phosphate and other salts
for dozens of brands. Interestingly, the liquid detergents all had
low salt levels, so the rule of thumb is to use liquid detergents
in preference to powders.