Cycling does not mean turning your tank into a toxic zone...

I've read an increasing fervor for dumping various things into a new tank to cycle it, many with the implication it does it faster---and some involving a lot of extra expense.

Cycling is a simple natural process of letting bacteria multiply and penetrate more than just the outer skin of your rock and sand. And bacteria multiply quite nicely without your doing more than setting up with one live rock amid conditioned (saltwater soaked) plain rock. I've even done it with no more than one gallon of lfs wastewater, dry sand and 100 lbs of completely dry rock. Twelve weeks later --- cycled.

The catch in all these schemes is very simple: time. No matter what you do, bacteria are not going to multiply their way INTO the rock any faster than bacteria can do it. Cured plain rock helps: it comes in having been wet and submerged for a lengthy time, and that probably helps the bacteria make a little faster progress to the inside, but rock being rock, those cracks, holes, and crevices are many, and it still takes time.

The notion that you are ready for a whole fish population the minute you get the chemical signal of a bacterial process is Not So! You are ready, at that point, for a cleanup crew---which is a gross misnomer. The real job of the cleanup crew is just to poo. Eat and poo. And you should start with a few a first and work your way up to a larger group. This feeds your sandbed and rock bacteria, helping them increase and go on multiplying. About four weeks on, you can put a fish in safely, granted you started qt'ing said fish when you started your cuc to work.

Is cycling supposed to be lethal? Not actually. I've more than once cycled with rock that had a heavy population of worms, snails, soft corals, even stony coral, sponges, and crustaceans, yes, and a few aiptasia and asterinas, which are a piffle in the process, pretty easy to treat, especially in a tank where they're not the only life: I keep aiptasia in my fuge, just because they're there, but they don't survive in my dt. One particularly nice load of rock had 52 separate species of critter come through the cycling process.

My standard method is, for a 50 gallon tank, set up and bring all equipment live, to establish the heating as it will be once ready: lights, skimmer, everything. I add enough flake fishfood daily to cover your two thumbnails. You don't even need to do that much, because most rock has crud enough to keep them going, but hey, maybe it will help keep hitchhiking critters alive, which I personally want to do.

And I wait. A secret of chemistry is that it slows down when water is cold. It can heat too much if water is too hot. Like Goldilocks, it works best if you keep that tank 'just right' in temperature, salinity, and, in short---doesn't it make sense?---'just right' in the way you want that tank to operate forever. Right temperature, right salinity, right flow, right everything.

You can add all this magic potion stuff, you can toss in dead shrimp and have an aroma to the process, and you can dance around your tank by the light of a quarter moon...but the main thing you can do to keep your bacteria thriving is provide a) enough rock and sand for the tank size b) a warm, stable water condition that's just like what they're going to be living in, and c) enough time to do their thing.