What does it mean if the top of your fish tank filter is making bubbles?

- The water level in your tank is too low. The water level should be high enough to cover the filter's intake and output tubes. If the water level is too low, the filter will not be able to draw enough water in to filter properly, and the bubbles will be a result of the filter sucking air instead of water.

- The filter's intake tube is clogged. If the intake tube is clogged, the filter will not be able to draw water in properly, and the bubbles will be a result of the filter trying to draw in air instead of water. To fix this, you can clean the intake tube by removing it from the filter and rinsing it off with water.

- The filter's output tube is clogged. If the output tube is clogged, the filtered water will not be able to flow back into the tank properly, and the bubbles will be a result of the filter trying to push the filtered water back into the tank. To fix this, you can clean the output tube by removing it from the filter and rinsing it off with water.

- The filter's impeller is damaged. If the impeller is damaged, the filter will not be able to circulate the water properly, and the bubbles will be a result of the impeller not being able to create a strong enough current. To fix this, you will need to replace the impeller.

If you have checked all of the above and the problem persists, then it is possible that there is a problem with the filter itself. In this case, you should contact the manufacturer of the filter for assistance.