Quick story, I did a 90% water change because the tanks gravel hadn't been cleaned in years. I added back water with conditioner, and some salt. Its a freshwater tank and I'm using the same filter(cleaned), gravel, plants, decor, and fish. My question is at what pace I should add the fish back at and If my tank will cycle again at a lethal level to the fish? I only have guppies, bristlenose plecos and snails. I've let a tester fish and snail swim around for about 24 hours and they're perfectly fine. Thanks for your time.