One thing to REALLY keep in mind is that many (MOST) skimmer manufacturers overrate their skimmer's capability. ASM and Euro-Reef are very similar in design, (Long story short...two guys started ER, one left and started ASM...ASM uses a less expensive acrylic and a slightly different neck union....thats the difference) but if you compare similar skimmers, (IE body diameter and pump) you will find a difference in ratings. For example:
ER CS6-2+....24 inches tall, 6 inch diameter body, powered by either Sedra 5000 or the Dolphin DP 1117, (ER uses both of these interchangably and refers to either one as the SP2.)
* rated for a 125 gallon tank.
http://www.euro-reef.com/skimmers/all.html
ASM G-3....25 inches tall, 6.5 inch diameter body, powered by Sedra 5000,
rated for 250 gallon tank.
http://www.globeaqua.com/asm.html
I seriously doubt that the extra 1/2 inch of width in diameter and 1 inch in height will double the ASM's capability over the ER.
I know that ER recently (last year or two) lowered the ratings of their skimmers, I suspect that ASM is using the old ER standards of ratings, and is a bit optimistic on their rating system. This is not a bash of ASM products, IMO ER cant necessarily be trusted either. Protein Skimmer ratings need be treated like Political promises on Election years.....not to be taken at face value.
IMO the best way to determine what your skimmer is really rated for is the flow rate through the skimmer itself...
http://www.superskimmer.com/skimmer_math.htm
One thing to note about this link is that they goofed when they posted up the calculations to measure your skimmers capability...
as per the link. It should be
Total gallons filled (divided by) Seconds to fill (x)
3600 = Skimmers GPH flow rate
When shopping for a skimmer I asked about this because I had a limited space available for my skimmer to be placed in, and I wanted to get as close to 4 times an hour system turnover through my skimmer as possible.
Here is a link where Jeff Mecare states the Sedra 3500 pushes approximately 250 gallons per hour with air being sucked in to create bubbles, (this will slow down the flow rate significantly as the Sedra 3500 is rated for 350 GPH and delivers 250GPH when hooked to the skimmer)
http://www.reefcentral.com/forums/showthread.php?s=&threadid=464777
Based on that info, my 75 gallons of total system volume is being processed by my skimmer 3.33 times an hour...not ideal but sufficient for now. I plan on purchasing a sedra 5000 in the future to bump that up to about 4 times an hour total turnover.
Hope this helps and isnt too confusing.
Nick
* I emailed Jeff Mecare of ER and asked him about the two pumps, This is the email he sent back to me:
euroreef wrote on 11/13/2004 05:37 PM:
It's ER terminology. We currently use two different suppliers for pumps so we use one "ER" part # so as not to confuse people.
-ER