ULNS (?) is a type of system? here is what one author thinks of that:

[waverider]

https://reefbuilders.com/2009/10/29/ulns-load-detritus-ultra-nutrient-system-desert/

ULNS is a load of detritus: an Ultra Low Nutrient ‘System’ is a desert​

Ultra Low Nutrient System or ULNS is a load of crap made up by people who don’t understand the words “Ultra” and “System”. The ULNS moniker was pulled from the ether with no understanding of how a reef ecosystem works. We are skewering the concept here and now because the name alone is totally misleading about what is really going on in a natural reef as well as an artificial reef aquarium system. Just to get the simplest part out of the way, the word System is defined as a set of interacting or interdependent entities forming an integrated whole. When an entire system is characterized by Ultra low nutrients, it is usually in reference to a desert or the open ocean, and outer space probably counts too. Both deserts and the open ocean have ultra low nutrients and they are both characterized by a very low amount of productivity and therefore nearly devoid of life. Contrary to what ULNS tries (and fails) to describe, a reef and a reef aquarium are both very high nutrient systems with lots of thriving life and a high productivity rate. So why then are misguided aquarists using the term Ultra Low Nutrient System to describe their reef tanks? Because amateur reef aquarium writers began using the term ULNS to describe the nutrient state of reef aquaria when a cursory review of the scientific literature would have yielded the word ‘oligotrophic‘; an elementary ecological term used to describe a state of tight nutrient cycling. Although it is true that a healthy reef ecosystem has low nutrients in the water column itself, there is actually a high level of nutrients being cycled and sequestered in bacterial processes, phytoplankton, and the whole food web that follows. This no-holds-barred rant has been brewing for quite a while but it was triggered by the Grumpy Old Reefer and his recent write up denouncing the Ultra Low Nutrient System moniker for it’s inaccurate description of what “Ultra” actually means. We highly recommend reading Grumpy’s comparison of aquarium and natural reef nutrient levels and let’s hope we can lay the inaccurate and misleading ULNS terminology to rest once and for all.

 

[blasterman]

Some of the best reef tanks I've seen were ULNS regardless of semantics. Their biggest advantages being they were quicker to get to stability over high import high export and didn't require several mortgage payments worth of fish. The later is increasingly become impractical with fish bans. ULNS just has a razor thin envelope.

Our home reefs are not natural reefs. Bacterial loads are totally different.

 

[Nano sapiens]

While I do enjoy the ReefBuilders content, Jake does sometimes tend to go off on rants every now and then

https://reefbuilders.com/2019/10/07/sponges-dont-belong-in-a-reef-aquarium/

The premise that tight nutrient recycling occurs on the natural reef is widely accepted, but the degree to which this contributes to the high net productivity is now known to be not be as restricted to the reef proper as once thought. Externally derived resources, such as endo-upwelling of nutrients (atolls), nutrient input from nearby reef associated environments such as mangrove forests, seagrass beds, land-based runoff, etc. (inshore) and low concentration but high total volume of oceanic nutrients (largely in the form of planktonic micro and macro organisms) are all significant contributors to a reef's productivity.

In the reef hobby we tend to use the term 'Oligotrophic' to describe a 'marine desert' with very limited nutrients on the natural reef, when the term is more correctly applied specifically to an oceanic reef's water column only (not the highly productive, but tightly nutrient recycled, benthos):

https://www.sciencedirect.com/topics/earth-and-planetary-sciences/oligotrophic-environment

The essential elements of oligotrophic environments are low concentrations of mixed substrates and concomitant low cell concentrations of a highly diverse indigenous microbial community, which grows slowly with relatively low visible activity. Certain conceptual, experimental, and methodological challenges arise from working in low nutrient environments, most notably the challenge of accurately detecting biodegradable organic carbon concentrations and the entire indigenous microbial community.

So what is the takeaway for reef aquarists? I do agree with Jake that the ULNS is not totally accurate as it really only applies to the oligotrophic condition of the water column itself and not the reef system as a whole. My understanding of these 'ULN' systems is that the various nutrient inputs regularly added are intended primarily to maintain and stimulate benthic productivity (including coral, with reduced zooxanthellae content to accentuate coloration) and thereby attempt to more accurately replicate a pristine oceanic reef environment.

 

[Scdell]

Good luck changing anything. Once a moniker sticks people run with it. Right, wrong or in between. Phosphate and Nitrate aren't really "nutrients" either. They are building blocks so to say.
I too yearn for the old days when there wasn't so many "know it all" instant gratification people in the hobby.

 

[Nano sapiens]

Phosphate and Nitrate aren't really "nutrients" either. They are building blocks so to say.

True, but like 'ULNS' nearly everyone now uses 'nutrients' as a descriptor for phosphate and nitrate...so it's 'stuck like glue'

 

[Nano sapiens]

I too yearn for the old days when there wasn't so many "know it all" instant gratification people in the hobby.

The conditions when I started reef keeping back in 1985 were indeed quite different and I do miss the more experimental DIY mindset. The flow of information was so much slower when waiting for the newest edition of a reef magazine or the weekly/bi-monthly visit to the LFS. All of which cultivated patience and promoted a more contemplative thought process compared to today, IMO.

 

[Scdell]

The conditions when I started reef keeping back in 1985 were indeed quite different and I do miss the more experimental DIY mindset. The flow of information was so much slower when waiting for the newest edition of a reef magazine or the weekly/bi-monthly visit to the LFS. All of which cultivated patience and promoted a more contemplative thought process compared to today, IMO.

Yep, information was really hard to come by back then. Products along with livestock were in short supply.
Sometimes you just had to get creative and try something or make something that worked.
Nowadays there's way too much information available and one has to sort out what's good and what's bad info.

 

[waverider]

The point of the article was that real ocean Reefs are Nutrient Rich environments full of a vast array of life. We strive for this in our home aquariums. Think about the entire chain of life it takes to make a stable reef aquarium: We prize Live Rock for its millions of organisms (pests aside), Live Sand, copepods, phytoplankton... shrimp, crabs... I'm striving to fortify my reef with an abundance of life. Yet it is a closed ecosystem so Nutrient control is necessary -to the limit of my system's ability to export. -Which is what Im striving to improve in my reef and what makes the hobby so fascinating. I wrote this post because I was reading the instruction label on one of my Red Sea care kits... it listed "SPS Tank".... "LPS Tank" "Soft Coral Tank"... then "ULNS" Ultra Low Nutrient System. ? I feed my reef, often.

 

[Timfish]

"When I see the colors of some of these low nutrient tanks, I can't help but be reminded of bleached coral reefs. It should therefore not come as a surprise that feeding corals in such systems becomes a very important component in these systems. Though reefs are often catagorized as nutrient "deserts" the influx of nutrients in the form of particulates and plankton is quite high when the total volume of water passing over a reef is taken into consideration.

Our crystal-clear aquaria do not come close to the nutrient loads that swirl around natural reefs. And so when we create low-nutrient water conditions, we still have to deal with the rest of a much more complex puzzle. Much like those who run their aquarium water temperature close to the thermal maximums of corals walk a narrow tight rope, I can't help but think that low-nutrient aquariums may be headed down a similar path." Charles Delbeck, Coral Nov/Dec 2010, pg 127

"Imported nutrients are usually transported to reefs from rivers; but if there are no rivers, as with reefs remote from land masses, nutrients can only come from surface ocean circulation. Often this supply is poor, and thus the vast ocean expanses have been refered to as "nutrient deserts". The Indo-Pacific has many huge atolls in these supposed deserts which testify to the resilience of reefs, but the corals themselves may lack the lush appearance of those of more fertile waters. Many reefs have another major supply of inorganic nutrients as, under certain conditions, surface currents moving against a reef face may cause deep ocean water to be drawn to the surface. This "upwelled" water is often rich in phosphorus and other essential chemicals." J. E. N. Veron "Corals of Austrailia and the Indo-Pacific" pg 30