Hi H2ose.
that TDS is way to high - at your PSI you should be able to get 15 TDS - no problem.
if you read the instruction manual ( which i didn't :

) there is a small sentence that states if you are
going to produce more than 50 lts of pure per week you should install another pre-filter ( sorry cant remember if its
sediment or carbon ) as the one inside the merlin wont cope with a higher volume.
i ran mine for six months without the extra filter and TDS went from 8 to 32 - changed merlin carbon filter & added extra pre filter and got it back to 18 and held that for over a year ( changing extra pre filter every 6 months )
Darran