Some additional thoughts on my "in must equal out" point above. hopefully it'll help OP to find his own long term success
I'm not saying that one method is better than the other, there are a lot of ULMS success stories (like
@Nano sapiens - great tanks btw). the key here will always be reaching that equilibrium point between what you put in and what gets taken out. A lot of the export mechanism also becomes more effective "the more the build up is" so even you don't do anything different, then "eventually" the tank will reach that "break even point" and equalize your in and out.
For example, assume you put in 10 "parts" of Nitrogen in the form of fish food per day. The 10 N is going to end up somewhere in your tank - maybe 2 Ns gets bind up in your biomass in the form of fish growth, that mean 8 Ns are flowing in your tank somewhere that eventually becomes 8 Nitrates. Then assume you do 10% WCs every week, in that 1 week, you have accumulated 8 x 7 = 56 of waste Nitrates, so, if 10% WC is all that you do, then you will have to accumulate 560 nitrates in order for the 10% WC to equalize the "out" with the "in". So what does 560 Nitrates mean to your specific tank? maybe not much in a large tank so ppm gets diluted down, but could be lethal in a smaller tank. In practice, WC is often accompanied by vacuuming the detritus, so the N taken out is likely higher than the 10% so it may not need to accumulate to 560, but the concept of "there need to be a critical mass of concentration before the out can equal the in" remains.
That's just one example, but every mechanism, whether is WC, or skimmer, or fuge, or DSB, etc,, has this similar concept of "needing to accumulate to a criticle mass". So the question becomes - where is that break even point and where is the "maximum" threshold point that your tank can safely sustain? If the break even point is lower than the maximum threshold, then you will have sustainable success, if not, you'll eventually have problems. Where that point is is different for every tank based on the waste profile, nutrient uptake profile, and biodiversity of the specific tank.
So, whatever methods you use, long-term success depends on getting to that "point" before your tank crashes. the dichotomy of "ULMS" or "nature/Bio" method, vs the traditional "extra filtration" method is highlighted below
1) the ULMS methods relies on increasing the biodiversity to increase the maximum threshold to allow for enough room for the "in" to builds up and reach the critical mass to match the "out". it also relies on having the right tank mates that can thrive in such conditions. Success stories often have the same below factors:
a) very judicious in feeding, to try keep the "in" as low as healthy for the tank mates
b) have the right tankmates - ie, softies/shrooms/lps will generally be more tolerant. Also majority of the biomass is is corals, which actually is an AMAZING sponge to absorb and lock up nutrient/waste into the biomass. Fish on the other hand, have a much more "dirtier" waste profile.
b) have big enough a biodiversity/biomass - look at the two ULMS tanks posted above - the both have a huge amount of both biodiversity and coral biomass relative to fish.
In theory, if the above is large enough and the maximum threshold is high enough, you can get away with "not doing any" export, where the nutrient eventually end up in coral structures and the coral outgrows your tank. at that point you'll have to frag out your coral to make room, and "fragging" becomes your export method.
2) the traditional method, on the other hand, focuses on increasing the "out" to match the "in" as quickly as possible to get to the break even point before the tank crashes. Not gonna go into detail here but this is your traditional skimmer/fuge/wc/etc... approach. one thing i do want to point out is that this method probably has higher chance of success if your tank mates and tank makeup is not compatible with the factors listed in point 1) above - ie, you have a lot of fish and not enough corals, or if you have corals thats sensitive to higher levels of waste - SPS, for ex.
So, where does that leave you? that's something only you can answer b/c you know how much you feed, you know what's in your tank etc, whereas our recommendations on what you should do is only dependent on the tidbits of information that you post here. Hopefully the above can help you focus on what you should be thinking about. Finding that "break even point" is not easy since we can't ready measure how much we put in, vs how much is taken out, vs how much is bound by biomass. Highest success is usually achieved by doing doing a combination of both - there is no harm in trying to increase your maximum point while also trying to increase the "out" to get to the break even point faster. Unfortunately, The only true indication, if you got to the breakeven point, is time; and the only indication that your "maximum" point isn't big enough is after your tank has a problem. But, at the end of the day, that's what makes this hobby so addictive right? as an OG in R2R (
@Paul B ) said - "reefing is not about the destination, it's about the journey".
whatever you do, just enjoy the process and have fun!
@BTimms - saw your question while i was typing my "book" above - sry if gave you the wrong impression, but i don't use DSB lol, partly b/c of the reason i initially gave that i'm not sure how P export would work there, and partly b/c i know it's not easy to maintain. My export is more of the traditional approach - I have skimmer and fuge. Fuge, in my mind, is one of the more effective methods not only b/c it exports both No3 and Po4, but it does it in a similar ratio as what you put in - (look up the redfield ratio, chaeto is about 16:1, which should be similar to the food you put in if you put in a high grade feed)
) is a powerful filtration system and will still require occasional maintenance. I strongly debate (and continue to do so) with myself on next tank system as I've always liked the concept of a plenum DSB.
