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.
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