I think that everybody knows that I am in the "availability over residual levels" camp. Feed a lot, export a lot and keep residuals reasonable, but low (not zero). Ammonium and ammonia are the prize to get nitrogen to SPS, not nitrate. A little bit of P is good, but not too much.
2sunny has a wonderful tank and has also posted lately about having very low residual levels but high throughput/availability.
I think that most people who have had N and P raise without dosing on the back end have seen the effect of more availability, not from having higher residuals. Their tanks would be just as good with the same feeding, but more fuge (or whatever). In nearly all cases, the availability does the heavy lifting.
Regarding low detection levels of nitrate, this is hard... my tank shows "clear" on test kits, but I have .1 to .2 on an ICP test. .1 to .2 is not zero and it is a world away. True zero is an issue, but you nearly always have to use chemicals or media to get there. My sandbed, which can chew through nitrates like crazy, always leaves enough to keep the equilibrium going forward.
Having higher levels of N and P can do other things for the tank, if you need them. They can poison dinos, matting bacteria and diatoms at levels that are not so high for most corals - some acropora will suffer at these levels, but most people just do with them and chalk them up to "too hard," which is smart. They also slow down coralline growth at higher levels, which is a plus to some. This is not the same thing as being ideal for SPS... but it does need to be incorporated into a whole-tank strategy.
You can get some deeper saturation with nigher N and P levels on some corals, but not others. Some acropora will have less differentiation in the colors if they are multi-colored, but not all. Most acropora with different colored growth tips will look better with lower N and P, but, again, not all.
I wish that more people understood that N and P are not food and are building blocks. I wish that more people understood that SPS cannot process nitrate without first turning it back into ammonia/ammonium at quite a cost of energy to the coral (we are in the SPS forum after all even though a few other corals can use no3 straight up). I wish that more people understood that dosing P is just binding more to your rock and sand with a very small amount ending up in the water column and that this could be a huge problem down the road. I wish that more people understood that lighting with the zoox making sugars is what truly feeds the coral and if they spend as much time worrying about wider spectrum (quality) over N and P that their corals would likely be a lot happier in most cases.
I do not care for a lot of BRS videos because they are more infomercial than real science, but check out their video on Zeovit, which is a heavy import and heavy export system - like 1:45 to about 3:30. They basically say that the tank has more "nutrients" going through it than any other tank that they have, but the backend numbers stay low. This is the goal, IMO.
I hate that they say Ultra Low since this tank is probably just like Natural Seawater and not Ultra Low. You usually have to use chemicals and media and not feed a bunch to get Ultra Low. IMO, natural seawater levels are just natural, not low or ultra low.
BTW - I do not recommend Zeo unless you are super into dosing and testing A LOT. However, it is an example of how high availability and low residuals do a great job.
Residual levels are the easiest - the values on the test kits of your nitrate and phosphate. These get focus since people can put numbers to them. They are also fools gold in most cases, like so many other simple things in our life... light weight of a human where one person weighing 225 is nothing but pure muscle and athleticism but is a lot of fat on others.
Availability is what what "in process" that the corals can use before it becomes nitrate at the end of the cycle. This is mostly in the form of ammonia/ammonium that the fish (and other things) have as waste product. This is nearly impossible to measure. It is a little more complicated than this, but this will do for now...
Bacteria can handle the no3 on the backend if you have a lot of good rock or sand that can harbor anoxic bacteria - these convert nitrate into nitrogen gas and keep no3 at good levels. Sometimes rock alone is not enough, but sometimes it is - just depends on the tank and the maturity of the rock. A 3 inch sandbed can usually take care of no3 in nearly all situations if it is mature and mostly left alone - there is some maintenance that is needed periodically which is more than we need to get into here. The new paradigm of starting tanks with sterile rock and sand mean that it can take years for them to act like real live rock from the ocean - their pores are usually bound with terrestrial organics and the bacteria have no place to live.
Phosphate is harder since nothing in the tank converts it to gas. Aragonite (sand and rock) binds phosphate and will act like a buffer (good) at low levels, but can also act as a reservoir (bad) at higher levels. You will need to grow macro algae, use GFO or other media to keep it low - water changes work, but are not efficient to lower P. It is important to understand the relationship between aragonite and phosphate and how much that it can bind - nearly all dosed phosphate ends up in the rock and sand.
There is another way that corals CAN gets some building blocks, but it is not clear that it happens in our tanks. Amino Acids. Amino Acids can be absorbed through SPS skin. This does not mean that dosing bottles Amino Acids will work. They are also used by nearly all single cell organisms on surfaces and in the water column. First, we have no idea which aminos are in a supplement - some are better than others. Second, it is losing math equation for the SPS to get some... the bacteria, single cell algae and other microscopic things in the water column and on the surfaces or the sand and rock will all want the amino acids that you are trying to give to your SPS. It is not likely that the SPS get much. While it is not likely that Amino Acid supplements do much for the SPS, the also do not seem to really hurt and maybe some of those microorganisms get caught by the corals (not in their polyps, but in their slime coat where they are dissolved and their energy/nutrients gathered). In the end, it probably does not hurt to dose some Amino Acids if your residual levels of N and P are in control, but you are likely hurting if your N and P are already high.
As always @jda I appreciate the depth of knowledge you bring to these conversations. I think you make lots of very valid points and provide your reasoning. I have seen @2Sunny ‘s tanks here and agree that the results he gets from a high throughput system are inspiring. I feel, like you do, that most starving coral situations could be better solved through increased feedings or more fish. The result you want with your tank has to match what is being put in. I also think that feeding the tank as a whole is part of what makes these heavy in heavy out systems successful. Everything in the tank from bacteria to fish has a chance to eat and acquire the proper nutrition at one point in the cycle. I also liked the way BRS explained the zeovit system. Too many people think that it’s as simple as stripping the tank of all N/P, but it’s so much more than that with the addition of all the food and elements in very controlled amounts. Overall I think some of the most successful full-blown acropora (not just SPS) reefs that I have seen have been simple systems, with tons of fish that get fed a lot and a decent skimmer and a big ball of chaeto. I’ve tried to overcomplicate my system in the past but I eventually went back to the basics of what I know best and my tank has thanked me for it.You can put me down as one of the supplement skeptics that have not ever seen one that did much in almost three decades of reefing. I am not saying that I have seen or used them all, but I have tried a bunch. I have no use for any of them and I can say with almost certainty that none of them are necessary at all. To each their own...
I also forgot to mention that hosts can recycle most things like N, P and aminos once they have gathered them for their symbionts. This means that it is likely that corals only need new stuff to grow, not just to maintain - this helps to explain why just a trace of building blocks are necessary. This has been debated by some, but also highly supported by others including some highly respected marine PhD folks. In addition to this resource below which talks about dinoflagellates inside of hosts, this recycling is mentioned in a few coral books that I own.
Nitrogen cycling in corals: the key to understanding holobiont functioning?
Corals are animals that form close mutualistic associations with endosymbiotic photosynthetic algae of the genus Symbiodinium. Together they provide t…www.sciencedirect.com
P.S. I know it’s the time of year for wish lists but that’s one big list!;Hilarious