When starting out as a saltwater fish keeper, most of us do this same costly error on our initial attempt at reef tanks. We purchase a protein skimmer that is sized exactly for the volume of the aquarium. Then, after several weeks, we find that there is no foam in the cup and water is cloudy. Nothing are wrong with the equipment. Rather, the equipment is not large enough for what’s actualy happening within that glass box. If you don’t know how to properly size your equipment, selecting a brand name with good reviews won’t help you.
Water chemistry is unseen until it fails. Most guides won’t tell you this, but here’s how I break it down into a simple multiplier system (see chart above). The size of your tank isn’t realy what you’re buying a skimmer for. You’re buying it based off the amount of waste your tank can potentially produce, which is typically about 50% to 100% larger than the tank itself. This additional capacity allow the pump to be powerful enough to churn away at organics before they become toxic as ammonia or nitrate. It also provides some buffering against your feeding regimen. Most folks over feed their fish by just a little bit each day, causing excess food to convert into dissolved proteins that cloud your water and stress coral. A well-sized skimmer will remove these compounds when they’re still floating freely around.
How to Choose the Right Size Skimmer
How do they work? Mechanically, skimmers uses the tendency for organic material to adhere to rising air bubbles. Millions of microscopic air bubbles is injected from the pump throughout the water column. As they ascend through the reaction chamber, proteins and lipids attaches themselves to the bubble surfaces. By the time the foamy mess floats to the top, it collapses into the collection cup allowing you to witness the removal of your tank’s waste in realtime. It’s satisfyingly tangible proof that something is actualy filtering. Getting sufficient bubble surface area to efficiently capture that waste is the trick. Stronger pumps and larger diameter necks (see comparison grid in infographic) are necessary on larger tanks because they have more volume then smaller tanks.
When it comes to deciding which skimmers to use, you’ll find that size guidelines vary based off contents of your tank. A highly populated tank of hungry predator fish creates far more waste than a lightly stocked coral-only aquarium. This means the former requires a skimmer sized at twice its volume while the latter can probably get by with a smaller, compact hang-on-back unit. Failing to account for this will result in purchasing a unit that’s always running and never removing any water. It seems like you’re doing more work than needed. On the other hand, a nano tank may be able to get by with a compact hang-on-back model because total quantity of waste is small enough to manage with a small pump.
The performance of any particular unit will depend somewhat on where it is placed as well. For example, skimmers mounted inside a sump tend to work better than other styles since they are hidden from view and has greater water column depths (more time for bubbles to float to surface and trap detritus). Conversely, hang-on-back units are handy when using small tanks without a sump, but is prone to instability when exposed to large fluctuations in water levels due to evaporation or manual refill. To prevent purchasing an inappropriate unit based solely on looks, the visual guide shows how each design fits into a variety of aquarium setups.
Remember: New stuff takes time. When a new skimmer arrives, don’t expect it to foam or even overflow until its first couple of days of use, manufacturer’s oils will be rinsed off the impeller, which is perfectly fine. Be patient. Break-in is part of break-in. Afterward you’ll notice a continuous stream of skimmate that’s tea colored. Tea means the unit is dialed in properly. It pulls the correct blend of dissolved organics while leaving beneficial compounds in the water.
So, at the end of the day, what’s the proper size? The answer is to plan ahead rather than reacting to problems in the future. Begin with one large enough to fit all fish you plan on keeping, plus extra (in terms of headroom) for how you feed them. Sure, you may pay slightly more now, but you would of had to replace equipment as soon as your initial skimmer dies due to being overworked by an overly stocked tank. Nothing ever goes wrong with good filtration… it’s boring.
