I thank everyone who has responded to my worries. Thank you Thank you
The quarantine tank is 40 gallons, no substrate. Filtration: AquaClear 110 (with a diffuser to soften current) and 2 large double sponge filters. Ammonia 0, nitrite 0, PH 7.4. I added API salt according to the dosing on box prior to getting the goldfish.
Last night I did a 20% water change. They were a tiny bit more active afterwards. I worried all night. This morning they were active and bright. 😃 What a relief!
Stress Guard definitely caused the fish to become mellow, to an extraordinary extent. I didn't realize Stress Guard could do that. If I ever use it again in the future I will use a much much smaller dose to start.
Thank you all once again!!