I have 4 tanks, never used water conditioner...I have lots of very happy fish, lots of egg laying and hatching. Even have shrimp which I use plain tap water. I just don't see the need in conditioner tbh I feel like its just another "buy me or you'll kill everything" product like test kits.
I understand it on a "macrobe" scale, all that chlorine would maybe kill a few but if its safe for us to drink along with pets. Then the Chemicals involved can't ever be at a level that's dangerous or degrading to Cellular structure.
I dunno just my Opinion, would be nice to know how many people use and don't use de-chlorinators and any noted issues.