Refuguims

Are they used to replace a skimmer? to say they are used to replace a skimmer is not accurate, could you use one instead yes, could you use one with yes. they are just a different filtration method
But are they good for also removing organic waste that skimmers remove?
they don't remove all organic waste products but they do remove some, and remove alot if you count removing what organic waste breaks down into. fish waste is even sold as fertilizer by a some companies. the big byproduct of fish is ammonia, plants consume it quite happily. so yes they are quite a efficient at cleaning a tank.
Can you have them lit for 24/7 or do they require a dark period for the plants to function properly? aww the question of the hour with plants, plants require darkness to go through hormonal changes that a necessary for sexual reproduction. BUT plants can grow vegetatively in 24 hour light just fine. We only need them to grow so a 24 hour light period which will boost growth is perfect for plants like cheato(asexual anyway) and may be mandatory for plants such as *caluerpa(which going sexual can have disastorous effects)
Given the choice of a refugium or a skimmer which would you go with?
you question is similar to if given the choice between a domestic car and a foreign car what would you choice. it depends if the foreign car is a lamborgini or a lada samara? is the domestic a amc pacer or corvette?

you see what im saying a good sized fuge could do more then a crappy skimmer, a great skimmer could do more then a fuge with poor plant choices.

generally they are used in combonation, most skimmers cannot remove everything and get you down to zero nitrates, but they can remove more waste then a fuge 10% dt could in a set period of time. most fuges for the standard 10% of dt size, cannot remove enough waste for a heavily stocked tank.

*i have been trying to get some data together to suggest if caluerpa cant go sexual in a 24 hr fuge, as of right now it is just a theory I have. based on the fact that land plants cant go sexual under 24hr light

 

Outstanding contribution from Sostoudt!
I use both a protein skimmer and a refugium for my tank and I use cheato in the fuge. This seems to work great for me. I do use reverse lighting as the fuge light is hooked into the moonlight timer. My cheato has quadrupled in size using this method.

Now comes the real question that only a scientist or chemist could answer? What if any trace elements are disapated by this method? Now of course I continuously add store bought trace elements plus mag, stron, iodine etc so I don't know this answer. Anybody out there with technical knowledge that can answer that so we that do use that method can properly put back elements that are lost.

 

i wouldnt expect it to be any more demanding then a coral would on elements except iron, phosphate, nitrogen, sulfur, potassium, and chlorine.
these are common ingredients need for fresh water plants
i wouldnt suggest replacing these elements intentionally as i dont think it is needed as long as you do water changes.
im sure it uses several other elements but only in small amounts atleast when compared to corals(exceptions would be calcified macros).

 

I dont think that one is better than the other, I believe they work hand-in-hand to provide better nutrient reduction.I've seen tanks with no fuge that look badass and the same without skimmers. Personally, I have both and am seriously considering doing away with the fuge, I havent harvested anything from it for months, theres just not much there to harvest.I run an opposite lighting schedule from the display to help with the PH but it doesnt do much. I guess the main reason for my fuge is to absorb the excess co2 from the cal. reactor. IMO once you reach a low nutrient system like for SPS then the macro doesnt grow very fast and becomes a mechanical filter like a sock. With a good enough skimmer it should be enough to process the waste. Now on the other hand for a "dirtier" tank i can see the advantages of having both.
Theres alot of other considerations to think about as well in choosing to skim or fuge, like how deep is the sandbed? how much live rock? how heavily are you stocked? hows your maintenance routine? IMO those are important factors in deciding the most effective way of filtering.

 

SoStoudt.. k+ for the "Fuge for dummies" read.. lol
I appreciate it not being so technical.