Before I start, I want to emphasize what follows is conjecture on my part offered to advance a conversation. I couldn’t really say I’m sure of anything and since I’m too lazy to refer to references, I could be plain wrong in places. I’m very interested in learning what here could be useful to future reefers and to improving it as best we can. I’m starting to get the feeling some sound advice is being misunderstood in a way that might cause tank problems. We’re hearing a lot these days about getting your nutrients too low. My concern is that people who have yet to get full control over their nutrients are taking this to mean they should be adding rather than managing. This lead me to thinking about just exactly how on establishes a reasonably stable equilibrium in a tank. The first time I thought about this I was trying to understand Zeo. ZeoStart, I’m fairly sure, is acetic acid and some nitrate compound. You’re dosing carbon and nitrate at the same time. The carbon drives down N and P and the additional N helps drive down more P. Here is where it gets interesting. Zeo is adamant you don’t need to do anything else to reduce phosphate and in practice, they’re right. Why? What if there’s not enough N? What if there’s too much? Turns out I don’t think it’s an issue. We know there’s a rough balance in uptake (Redfield, etc.). By adding more, it’s unlikely there will be too little. If there’s too much, your tank has other processes for taking up nitrogen that are underutilized in a clean tank. So your rock acts as a buffer against too much nitrogen. If Zeo is correct and the zeolite is reducing it as well, voila, stable equilibrium. Okay, so what if you’re not using Zeo? Let’s say you’re using chaeto instead? You crank up the chaeto growth and drive your nutrients down. Presumably when they get low enough one or the other will remain in excess. So you have to dose, right? Not so (let’s leave aside whether you need to dose for coral health, I’m just talking equilibrium here). You either end up with nitrate being too low or nitrate being too high (phosphate being too low). But your tank comes ready made to deal with either. If there isn’t enough phosphate, excess nitrate gets broken down in the rock, etc. if there isn’t enough nitrate, you get something that can subsist on organic phosphate. Cyano is a nitrogen fixing little bug. Far from being a pest, it’s actually working to bring your tank into equilibrium. If you’re pushing down the overall nutrient level sufficiently, it will do it’s job then fade away. Based on this you could predict the red slime phase tanks go through, the reason established tanks better tolorate high nutrients, as well as a lot of the other stuff we regularly experience. You should also be able to predict the amount of each nutrient in solution in a well established tank based mainly on the knowledge your removal exceeds your input and on the quantity you add. My point, for those insane enough to get to it, is that I think the correct advice is to eliminate your nutrients, then increase them a bit. Advising people to target a number leads folks who have not yet established an equilibrium to start chasing their test kits. It can work, but the system is unstable. An alternative to raising them once you get close to 0 is to run nutrient removal intermittently. As long as you’re running it enough to get everything out over the course of the day, the off cycles will result in plenty of opertunity for corals to outcompete your filtration while still maintaining a closer to natural environment (also interestingly consistent with Zeo directions).