that brings up another issue... I'm currently using straight RO water on "most" of my tanks I'm just completing a small hard water line taken before the whole house softener, to blend into shrimp & live bearer tanks... but that would be very hard water... during a power outage, our well doesn't run, so water changes would be challenging... I do pretty much keep a full barrel of RO water, that warms to room temperature, but even that requires a pump to move it from the drum to the tanks... one thing I've noticed, with all the plants, & using straight RO water, is that my water tests fine, for between 2 & 3 weeks ( the longest I've inadvertently gone between changes )...
so... during a power outage my water will probably be good for quite a while... granted maybe not for 2-3 weeks still testing perfect, with the pumps & filters not running... but at some point, I fire up the generator to run the well pump, & or heat & air conditioning, & refrigerators & freezers