How does soap affect fish?
Similarly, can soap kill fish?
Yes you do risk shocking the fish by doing this, but they should survive. Soap WILL kill them, so it's the lesser of two evils. Edit - changing 100% of the water WILL NOT cause an ammonia spike.
People also ask, is dish soap toxic to fish?
Under any circumstances and no matter how much dirty your tank is DO NOT use dish soap or any other type of soap to wash your tank in it's entire life. No matter how much you rinse there will be residue of soap on the internal walls of the tank and your fish will suffer and die because of this.
Adding soap lowers the water's surface tension so the drop becomes weaker and breaks apart sooner. Making water molecules stick together less is what helps soaps clean dishes and clothes more easily.