I know those new to the hobby sometimes make this huge mistake, and I know many (but not all) big box stores aren't stellar examples of good fish keeping practice/maintenance.
Nonetheless when I incidentally found my way to a Petco website tonight I was a bit shocked to see this super piece of advice in the Aquatics section:
How to Clean a Fish Tank:
Once you have set up your aquarium, it is important to keep the tank clean. When cleaning a fish tank, first remove the fish and place them into a smaller container. Remove all decorations and gravel and rinse them in clean water, then clean the sides of the aquarium with a sponge. Scoop out about half of the water in the tank and replace it with new water that is the same temperature. Then, return the decorations and fish to the tank.
Ooohkay, goodbye bb, hello

Nonetheless when I incidentally found my way to a Petco website tonight I was a bit shocked to see this super piece of advice in the Aquatics section:
How to Clean a Fish Tank:
Once you have set up your aquarium, it is important to keep the tank clean. When cleaning a fish tank, first remove the fish and place them into a smaller container. Remove all decorations and gravel and rinse them in clean water, then clean the sides of the aquarium with a sponge. Scoop out about half of the water in the tank and replace it with new water that is the same temperature. Then, return the decorations and fish to the tank.
Ooohkay, goodbye bb, hello
