If you have an AeroGarden that operates with an aerator/bubbler rather than a pump, it is important to check your water bowl occasionally to ensure there are air bubbles present in the Water Bowl. See the picture below for an example of the aerator in a water bowl.
If your model does not have this type of assembly in the center of the water bowl, then you do not need these instructions. Consult the Water Pump vs Aerator page for more information.
To test the aerator, remove the airstone from the tubing, leaving the tubing and the U-shaped holder in place. You may need to apply more pressure than expected to get the airstone off the tubing - it is a snug fit. Sometimes it just won't pull off, in which case scissors can be used to cut the airstone out of the tubing. You can see the tip of the airstone inserted into the tubing - cut just above the tip. There will still be enough length remaining in the tubing to keep the airstone submerged once replaced.
Once removed, you should see air bubbles pushing through the tubing. This tells you that it was indeed a clogged airstone that was preventing air from pushing into the water bowl.
If there are no air bubbles even with the airstone removed, it is possible that the aerator in the base has failed. If that is the case, please contact customer service.
If the air hose produces bubbles without the airstone, scrub the airstone with a soft brush (a toothbrush works well) dipped in either lemon juice or distilled white vinegar. Both are effective at dissolving and cleaning minerals from the airstone. Dip and scrub repeatedly to remove all the debris. You can also submerge the airstone in a small cup of the lemon juice or vinegar and allow it to soak for an hour or so before scrubbing for a more thorough cleaning.
Rinse well, and allow the airstone to air dry before reinserting into the tubing. Once replaced, you should see air bubbles in the water bowl. If not, and there were air bubbles coming from the tube without the airstone, then the cleaning did not open it up enough to allow air to push through, and it should be replaced with a new airstone.
You can purchase replacement airstones and air hoses online.
It is fine to run the AeroGarden without the airstone, but be mindful that the same debris that collected on the airstone can now collect in the tubing. If you choose to leave the airstone off, be sure to clean out the tubing between seed kits (or as needed) to ensure that air can pass through the tube freely.
It is a good idea to get in the habit of checking for air bubbles in the water bowl occasionally. The aerator provides oxygen to plant roots, and without oxygen the plants will slowly die off. So keep those bubbles bubbling!