slowly is the best way to lower
tds.
You see all the hype on acclimation;temp(which counts) ,ph,
gh,
kh all just boils down to
TDS for fish osmoregulation
IMO.
I really can't speak for specific parameters for cories but stated levels I use with my soft water fish for some time without issue.
You mileage my vary, but atleast for the eggs I would try to get lower.
Like I said I keep and sell all my rams in my tap(350+) but breed in 50-100...
Change slowly like 10-25% a day for a week to get where you want.
More smaller changes can happen multiple times daily
IMO but will cost you more in water do to dilution and small % of change...
Just pick a target and watch what happens!(How I roll!).
As far as distilled it should be just as good as
ro IMO just harder to produce.
I always bought distilled at Walmart before my
ro...
Good luck!
IMO the
TDS will NOT change like ph over a 24 hour outgassing...
This is why ph is bogus for what you need to get to....