this is really puzzling...

[RIPTANK]

Yeah, I kinda had the same issues. When I was using straight up tap water everything seem to be thriving but of course so did the algae. Then I switched to distilled water and everything I threw in died! Seriously, I lost 5 fish in a week.

My pH was too low and I was always adding buffers to get the alkalinity and pH back up. I seriously needed a doser for all my chemicals but just didn't have the set up and decided to go back to tap water again until I was able to accommodate a proper sump and doser. And now everything is fine again with just tap water... Just weird. Of course, I wouldn't recommend using tap water with any sps in your tank 'cause of the insane algae blooms but with softies no worries.