Bubbles FAQ
One of the most common problems with reef aquariums is bubbles in the tank. These bubbles come from two sources: from the filtration system and from chemical processes. Both sources will be discussed in this FAQ.

The Filtration System

There are several components of the filtration system that can lead to bubbles being returned to the main tank. The two main culprits are microbubbles from the protein skimmer and water agitation in the sump.

For hang on protein skimmers, the solution is not easy. Often the only approach is to build a barrier for the bubbles to pass through before they get to the tank. This is often a piece of foam through which water is forced to flow. Often the bubbles will be trapped by the foam. This is not an ideal solution as foam has a tendancy to trap debris as well and will need to be cleaned very often to prevent accumulation of detritus in the system.

Most other issues can be resolved in the sump. There are a host of other causes for bubbles in the sump: air is pulled down the overflow in most setups, protein skimmers may return fine bubbles into the sump, pumps may suck air from the surface, water agitation in the sump from the overflow causes many bubbles, fast water movement around (and particularly over) items in the sump often creates fine bubbles as well.

The solutions to bubbles in the sump are numerous but rely on three main principles: make the bubbles travel a long way, place obstacles in the bubbles way, and pull water from the bottom of the water column. You want to give the bubbles time to rise to the surface and burst. This is key.

The easiest solution, given enough room, is to place all agitation and bubble creators on one side of the sump and place the return to the tank on the other. If the distance is great enough, you will eliminate all bubbles.

The distance solution is not practical in most situations. You can achieve the same result by increasing the time is takes for water to move through the sump. This is most often achieved by creating a baffle system in the sump. These baffles are simply pieces of acrylic that the water must pass over and under as it moves through the sump.

A better solution is to add live rock to the sump. This is often a bit more expensive, but is much easier to implement in an existing sump than baffles and often works much better. Many commercial setups use foam blocks as a solution. This is not good. The maintenance required can be too much work. If left in place too long, these foam blocks can lead to significant water quality issues.

In order for the above solutions to work, you must be able to isolate the source of bubbles to one side of your tank. The final source of bubbles in the tank cannot be isolated this way. The return pump may cause bubbles in your main tank by sucking air from the surface in the sump. The simple solution here is to make sure the water level is maintained deep enough to prevent this (see the DIY section for water top-off designs).

A simple solution to reduce the frequency of this problem is to add a PVC elbow before the pump. This elbow should be installed in order to force the pump to pull water from the very bottom of the sump. This also helps with other bubble problems as well since the bubbles rise as they move through the sump.

The bubble issue can be tricky, but if you analyze your setup and determine the source of the problem, you should be able to solve it by applying the priciples outlined above.

Chemical Processes

You may find bubbles attached to your substrate, live rock, aquarium sides, etc. This is natural in most situations, but may be an indication of water quality problems. There are three main sources of these type of bubbles: microbubbles from the filtration system as described above, bubbles created by the nitrogen cycle, and bubbles created through photosynthesis.

Live rock and deep sand beds house bacteria which process ammonia into nitrite, nitrite into nitrate, and nitrate into nitrogen (source of bubbles). The sand beds are more efficient at the last stage. If everything is working properly, you will occasionally see small clear bubbles form on the surface of the sand bed or live rock. This is a good thing. If these bubbles stand and become coated with slime, this is a bad thing. You typically see this problem if you are in need of a water change.

Algae in your system may convert carbon dioxide into oxygen. When this happens, small bubbles often get trapped on the algae suface. Usually this is an indication of a slime film (a type of algae or bacteria). Again this is typically a sign of poor water quality indicating the need for a large water change. For more information on red slime see the red slime FAQ that we link to.