How are skimmers rated?

[Mythicalelf]

Like how do they decide a skimmer is for100 gallon aquarium?

Is it based on physical size?

Is it based on water that passes through it in a given time?

[whosurcaddie]

Usually its based on size. The larger the chamber the more micro bubbles the more micro bubbles+longer contact time = higher volume of skimmate.

[julie180]

Its a good idea to get one rated for higher than your tank volume.

[RocketEngineer]

In reality, there is no "standard" that companies follow. They can say whatever they want for tank size and nobody is going to be able to do much about it. Some companies make a concerted effort to be accurate while others seem to work off the "close enough" method.

On the other side of the coin, each reef tank is different. Different fish, different corals, amount of rock is unique, sand or no sand. The number of variables is huge so accounting for all of them is just not going to happen.

Where does this leave you? Buy a skimmer that is rated for a system larger than yours. Keep in mind that skimmers work on protein concentration so if you have few fish/corals you aren't likely to get a lot of foam production. Keep an eye on it as you add more livestock as the production rate will change with changes to the tank including coral growth.

And remember, a skimmer is just one part of the filtration plan. Water changes are another. Don't neglect either.

HTH,

[SGT_York]

Skimmers are rated based on what manufacturers think they can get away with.
Flow rates and size are indicators but there is no correlation or guideline that is followed.

I have a light fish bio load so am comfortable with a skimmer about 15% over capacity. Tank is 180G skimmer is rated at 210.

[Sk8r]

Some styles of skimmer produce more bubble froth than others. My Coralife has a knobbly rubber impeller-sort of thing that whips up a lot of froth. My Aqua C had a no-moving-parts system that took in air and ran bubbles (fewer and larger) into a chamber.
Look into the mechanics and get as much froth for the price as you can, but within reason. If you're running sps corals, which live mostly on light, you need a hyper-efficient skimmer and very clear water. If lps or softies, the corals themselves will prefer less efficiency. They derive more of their nutrient from water.

[coralsnaked]

Ratings being what they are most Venturi style skimmers are rated at 15% of the total water volume of the pump. IE a skimmer w/ a 950 GPH pump should be rated @ ~ 150 gals. ...most are rated with term "up to" meaning the maximum gals the skimmer will perform in with a medium bio load in a fish only tank. You can multiply that by 0.67 for a soft coral tank and by 0.34 for a stony coral tank.

But the bottom line is this + the dynamics of each style make some skimmers more efficient than others. The shape of the skimmer design and the size of the bubbles are equally both important, So one skimmer with the same rating may out perform another with the same rating.

[Mythicalelf]

And I'm guessing the smaller the bubbles the better?

[RocketEngineer]

And I'm guessing the smaller the bubbles the better?

Yes. Smaller bubbles have a higher surface area to volume ratio and since the proteins we are trying to remove congregate at the air/water surface, small bubbles mean more proteins removed.

[Timfish]

I stopped using skimmers in the mid '90s and haven't regretted it.
http://youtu.be/_Uf5IyXvajg
http://youtu.be/KhcRz50cV0s
There is no metric used by aquarium skimmer manufacturers even though research by Feldman, et al, identified two different methods skimmers can be compared. What's more recent research by Rohwer (Coral Reefs in the Microbial Seas) and others show that DOC is the real culprit in reef degradation and corals death, not nitrates and phosphates. The best way to get rid of DOC is with water changes. Feldman's research shows skimmer are very poor at removing DOC. Here's links to Feldman's research on GAC, TOC and skimmer performance.

http://www.advancedaquarist.com/2008/1/aafeature1

http://www.advancedaquarist.com/2008/2/aafeature1

http://www.advancedaquarist.com/2008/8/aafeature3

http://www.advancedaquarist.com/2008/9/aafeature2

http://www.advancedaquarist.com/2009/1/aafeature2

http://www.advancedaquarist.com/2010/1/aafeature

http://www.advancedaquarist.com/2010/2/aafeature

http://www.advancedaquarist.com/2011/3/aafeature

[ReefsandGeeks]

+1 on no "standard" measure for ratings. Each company has their own system for the ratings, whether it's theoratical based on dwell, bubble size, flow rate, air rate, skimmate produced...etc or if it's tested physicaly with some sort of set up to see how much skimmate of a certain quality they can remove...or maybe they just guess? Point is, each company is likely consistant, but a rating of 75 gallons from reef octopus isn't the same as 75 gallons from Esshops, or any other brand. Just do what most people do, and pick a reputable brand and get a skimmer rated for 50-100% more than your setup.