To clean your aquarium, you should never have to remove all of your fish. Remember, we're doing regular maintenance. We're cleaning the tank every week, every two weeks, every three weeks. You never want to shock the entire system. Removing the fish is shocking the system. Let's leave the fish in the tank. Change 15 to 20 percent of the water, gravel clean the sand, clean the filter. Try to break up the cleaning practices, so you're doing the filter one week and you're doing the water change on the other week. That will minimize stress. All of these practices require that you leave the fish in the tank. You don't want to have to take the fish out.
The only time you have to take the fish out is if you've neglected the tank to the point where you've got a bloom of hair algae or anemones to the point where it's easier to scrap everything and start from scratch. In that event, you take the fish and water out, and then just clean the heck out of the tank. You clean the rocks, change the sand, basically start the tank from new and then add all the fish back in. You should never have to remove your fish when cleaning your fish tank. You really, really shouldn't. It's only going to stress them out. You want to do regular, regular cleanings. Clean the algae, do the water change, and all these things require leaving the fish in the tank.