i was adviced against using crystal pro for large water changes as well..
at that time when i was shifting my LS from old tank to my new tank,
i was using more than 200l of "filtered" water only to realise that after my 3rd pail of water,
i tested the PPM and it was something like 120ppm, way above some of the normal tap water readings.
oh well, that was because my old resin was already giving out about 50ppm water before that,
and i thought after that large water change i would change the resin..
didnt know that it would shoot up so high...
anyway, i'm still using crystal pro for my 2ft..
sometimes i would just get NSW if i pop by iwarna..
but i agree with the rest, should use NSW for large water changes in the longrun..
but of cos if you're getting a RO unit, thats another case which is different altogether