Testing low nutrients doesn’t mean there are low nutrients in the system... rather, It means there is a low amount of accumulated nutrients dispersed in the water.
Many of y’all probably have experience with mass balances in one form or another. But for those that haven’t:
accumulation = Input – output + Generation -Destruction
In this simplification, we are looking at the water, then coral food and fish waste are our inputs, and corals and algae taking in the nutrients are our output. To keep things simple, we can ignore generation and destruction for now. To interpret this, if accumulation is low, it does not mean that our inputs are low. All it tells us is that our outputs are matching our inputs. This is called being at “steady state”. If there is an imbalance, then accumulation will increase. Most systems will adapt to a steady state environment, which is likely why natural reefs, with their great biodiversity, are quick to get back to 0 accumulation of nutrients.
Maintaining a low accumulation that is within a safe range is not bad (in my opinion). Conversely, having zero accumulation does not mean that your corals are receiving less food (I.e. You can have equal output in either scenario). However, at steady state, you could potentially be creating a limiting nutrient and thereby not maximizing growth. This is not necessarily a bad thing though either, and does not mean that growth is being restricted/capped. It is a fair analogy to think of this as ’possibly regulated growth‘. However, growth/color/etc could potentially still be maximized... It just notes that both options become a possibility in this case.
I run a ULNS.
- Nitrates test undetectable (<0.25ppm)
- Phosphates are usually around 10-20 ppb lately
- I don’t feed coral hardly ever. Maybe once or twice a month, if I feel like it.
- Not a heavy bio load (some damsels, a goby, a basslet, and 1 young Tomini tang in a 120g display)
- Fish feeding is maybe 5-6 days a week, once per day, in the morning, frozen food mostly, occasionally pellets
- No major algae issues. I had some turf algae that was starting to grow. Given that nothing really likes turf algae, Vibrant recently came to the rescue to wipe it out before it got bad.
- Corals look great! Amazing color all around. Softies, LPS, SPS including 1-2 dozen designer Acros and multiple anemones. Everything also has good polyp extension, and good growth.
Hope this data helps! Great thread