After your plants finish their growing cycle then you might need to clean the water tank.
To accomplish this, you can take off the lid and open up the water tank for better access.
First, you will need to remove the lamp but make sure the extensions stay on.
Then you can grab the bottom parts of the extensions, gradually bend inwards and start to lift (similar to a see-saw) the lid off - voilà! The lid is off and you can clean the tank as you see fit.
When putting the lid back on then make sure you don't leave any visible gaps.
For a better look, check out this video: