Protein Skimmers are fairly simple devices to install but getting the best performance out of your protein skimmer takes a bit of understanding. They are not plug-n-play devices and require that you tune the skimmer to your particular level of nutrients in order to optimally remove those nutrients. A skimmer that is not tuned properly will remove nowhere near as much waste as a skimmer that is properly sized for the aquarium and tuned correctly.  Furthermore, you may need to adjust your skimmer over time as nutrient levels change in the aquarium.

3 Variables For Tuning a Skimmer

There are really only three variables that you can control to affect a skimmer's performance beyond choosing an appropriately sized protein skimmer for your aquarium.  When it comes to choosing a skimmer, always veer on the smaller side if your tank is right on the edge of a tank size rating.  Undersized skimmers will always work but a grossely oversized skimmer can be nothing but a micro-bubble machine.

Sump Water Level Outside The Skimmer

Most skimmers come with a recommended water depth, that is the depth of water outside of the skimmer or "submersion depth".  By adjusting the submersion depth or water level within the recommended range, you are subtly changing the amount of head pressure on the pump which affects how much air is being drawn into the skimmer. The amount of air being drawn into the skimmer determines the foam density but the room for adjustments is usually quite small.  

  • Deeper water level = less head pressure = more air
  • Shallower water level = more head pressure = less air

Foam Level Inside The Skimmer

All skimmers have a foam level adjustment, typically a valve right on the drain. As you close this valve, it will cause the foam level to rise inside the skimmer body. As you open this valve, the foam level drops inside the skimmer's body. This adjustment does not affect the density of the foam, it really just negotiates how fast or slow you collect those bubbles in the cup.

Amount of Air Via Venturi

The amount of air going into the pump affects the density of the foam and is the most critical adjustment. Most AC pump-driven protein skimmers do not provide a way to control airflow so you are somewhat limited to the minor adjustments you can make to the water level or add an air control valve to the venturi airline.

DC pump-driven protein skimmers allow you to control the pump speed which then negotiates how much air is being pulled into the skimmer and, therefore, provides you with a wider range of air tuning abilities. 

  • More air bubbles = denser foam = wet skim
  • Less Air = less dense foam = dry skim

Air To Waste Ratio

When tuning a skimmer, it's all about finding the right ratio of air draw to nutrient level. Assuming the nutrient levels in your aquarium water are fairly constant, it's just a matter of tuning your skimmer to consistently pull the right amount of air and create the optimal foam density for maximum waste removal. 

  • If your skimmer is constantly overflowing with fast-rising bubbles that fill up the cup very quickly with water, it's too much air for the amount of waste in your water. The microbubbles cannot retain their shape, they quickly aggregate, rise, and pop filling the collection cup with water. (most common issue)
  • If the foam head is thick, full of chunks, and not reaching your collection cup, it's likely not enough air for the amount of waste in your water. This is a pretty rare scenario considering most modern internal skimmers are quite efficient in terms of air draw. Raising the internal foam level is likely the answer moreover trying to increase the air.  

Keep in mind that larger skimmers pull more air and if you cannot seem to stop your skimmer from overflowing regardless of water and foam level adjustments, it's probably oversized for your aquarium. An undersized skimmer, on the other hand, can be tuned to pull a stable foam head. The cup would just fill up faster and it won't pull as much waste as a larger, more appropriate skimmer would. Point is that everything starts with choosing the right size skimmer.  

Finding The Balance

Ultimately, the goal is to find that balance where the amount of air drawn into the skimmer is creating the desired foam density, resulting in a consistent collection of waste in the collection cup. The foam head should be stable, hold its shape, and rise slowly into the collection cup. It will be slightly discolored, there should not be any chunks and only a fine layer of mud building up on the skimmer's neck over the course of 5 - 7 days of skimming.

After stabilizing that foam density via air adjustments, the foam level adjustment can then be used to adjust how fast you collect that waste.  

How to Tune an AC Pump Internal Skimmer

  1. Verify the water level in your sump is within the recommended range outlined by the manufacturer. You can raise your skimmer using a skimmer stand or pieces of louver egg crate.
  2. Adjust the internal foam level using the outlet pipe to 50% open.
  3. Let the skimmer break in for one week. During this time the skimmer will probably overflow or act erratically, this is normal. Rinsing a brand new skimmer in RO/DI water before installation will remove any oils or manufacturing residue and helps to alleviate these effects. Regardless, give it one week before attempting to really dial it in to be safe.
  4. If needed, adjust the airflow to achieve the desired foam density. You can do this by adjusting the submersion depth (within the manufacturer's recommended range) or adding an air valve to the venturi airline.
    • Large bubbles that rise fast and fill the cup with water = too much air (most common)
    • Slow bubbles that fail to rise into the cup and cover everything in mud = not enough air (rare scenario)
    • If your aquarium is very new with minimal organic waste levels, reducing the air may be required to get the skimmer working consistently.  If the aquarium is heavily stocked with higher waste levels, the skimmer probably won't require any air adjustments as long as it is properly sized. 
  5. Adjust foam level using the outlet pipe to control the rate at which you collect skimmate in the cup. It's best to start with the foam level even with the bottom of the skimmer neck and let it climb into the cup on its own. If it collects too fast or overflows, reduce the foam level by 1" and evaluate again after 24 hours. Repeat until you are collecting waste as desired. 

How to Tune a DC Pump Skimmer

  1. Verify the water level in your sump is within the recommended range outlined by the manufacturer. You can raise your skimmer using a skimmer stand or pieces of louver egg crate.
  2. Adjust the internal foam level to its lowest position, 100% open outlet valve.
  3. Let the skimmer break in for 5-7 days. 
  4. Adjust the pump speed to achieve the desired foam density which is probably somewhere in the middle of the flow range settings. Slowing down the pump reduces the air draw. Speeding up the pump increases the air draw. 
    • Large bubbles that rise fast and fill the cup with water = too much air (most common)
    • Slow bubbles that fail to rise into the cup and cover everything in mud = not enough air (rare scenario)
    • If your aquarium is very new with minimal organic waste levels, reducing the air may be required to get the skimmer working consistently.  If the aquarium is heavily stocked with higher waste levels, the skimmer probably won't require any air adjustments as long as it is properly sized. 
  5. Adjust the internal foam level to collect waste as desired. It's best to start with the foam level even with the bottom of the skimmer neck and let it climb into the cup on its own. If it collects too fast or overflows, reduce the foam level by 1" and evaluate again after 24 hours. Repeat until you are collecting waste as desired.