The main thing about the skimmer chamber that matters is that it recieves raw tank water, completely unfiltered and to make sure it does not keep recycling the same the water it just processed. IMO and expericences algae scrubbers(using chaeto as the macro) do much better under higher turnover rates than the 8X-10X you recommend. In my system I have 600 gph going through my fuge which is a 20g with roughly 15g in it while operating. Thus my turnover is 40X, but not all parts of the fuge chamber actaully see 40X just by the mere design and use of baffles. The places that do see a lot of high laminar flow always grow the fastest and greenest. So I went and put chaeto in between my first two baffles before my actual fuge chamber(very high turnover rate in between the baffles) and it grows twice as fast as the chaeto in my fuge does. I am referring to laminar flow however and not linear flow with a powerhead in a fuge blasting straight at the macro.
As to why you need to send raw water to a fuge, you don't. Fuges and skimmers do not compete with one another at all. They each perform completely different functions. Skimmers take out proteins before they have a chance to break down and enter the ammonia cycle. They do not take nitrates/phosphates out directly at all. Through the use of Kalk, skimmers can help precipitate PO4, but that is another thread. Of course fuges do nothing to take out proteins. Point being they do not compete with one another at all, so why do people feel you need to send raw(dirty) water to a fuge?
The main problem with the split design in IMO is most just dump water straight in with no settling chamber, or baffles to have laminar flow over the whole fuge, not just one area. All this allows is detritus to build up that would have otherwise been skimmed out of the first chamber had the water been sent to a skimmer first.
A few quotes from Anthony Calfo...
""Thus... for Chaeto in a 20 gall 'fuge... a 400gph flow (20X) is not asking a lot. Its not enough flow in many cases (like when significant particulates enter from incoming water). In such cases where aquarists get misled to use the old slow-flow recs (under 10X)... it is no wonder the refugium becomes a cess-pool of nuisance algae.
Slow flow in most any refugium (other than settling chamber styles that are actively serviced) has been one of the single biggest tidbits of "mythinformation" promoted at large in recent years. Its patently bad husbandry IMO.
Anthony"
And on the subject of feeding "raw water" to a fuge instead of skimmed water to a fuge here is some more info from the same author on this subject...
"above all things else... the skimmer needs to get all raw water first. Otherwise, organics that you would prefer to be exported are allowed to linger as sediment, get tied up in refugia otherwise, etc.
Be very direct about aggressive skimming and supply it with first chamber raw water."
