waterdrop
Enthusiastic "Re-Beginner"
Yup, "percentage" changes don't really have much meaning during fishless cycling, its better to just change the largest amount practical. For me that means changing all the way down (about 90%) until if I went any lower I would let air get into my external cannister intake (I'm too lazy to turn it off usually during a water change, so it just makes a nice waterfall out the spraybar while I'm changing. Of course, heater needs to be unplugged if its going to be uncovered.)
If the tap water will then raise the pH up to a pretty good level (something higher than 7) then that's probably a good enough method without introducing baking soda, but of course baking soda can also be used. Its unknown whether the kickstart a stalled fishless cycle can sometimes get from a water change is totally due to the raising of pH or whether there might be other factors at play. Adding fresh tap water does add a little calcium and iron, both of which are known to be used by the autotrophs, but levels needed are not known other than "trace."
~~waterdrop~~
If the tap water will then raise the pH up to a pretty good level (something higher than 7) then that's probably a good enough method without introducing baking soda, but of course baking soda can also be used. Its unknown whether the kickstart a stalled fishless cycle can sometimes get from a water change is totally due to the raising of pH or whether there might be other factors at play. Adding fresh tap water does add a little calcium and iron, both of which are known to be used by the autotrophs, but levels needed are not known other than "trace."
~~waterdrop~~