There are a few things you can do to clean fish tank gravel without using a vacuum cleaner. First, use a plunger to suction onto the gravel and pull until the gravel is dislodged. Second, use a vacuum cleaner with the hose attachment to suck the dirt and debris out of the tank. Finally, use a bucket or other container to pour water into the tank and stir until all of the dirt and debris is completely removed.
