Cycling means growing the filter bacteria that convert toxic ammonia into nitrite, and then into far safer nitrate, before any fish move in. Bacteria need feeding to grow, and their food is ammonia itself — which is why a fishless cycle needs an ammonia source you supply deliberately. The sources differ in one important way: how precisely you can control the dose, and since the whole process is steered by test readings, control is what you are really choosing.
Pure ammonia solution: the controllable option
A plain ammonia solution — ammonia and water, nothing else — is the source most fishless cyclers choose, because you add a measured amount and confirm the result with a liquid test kit, commonly aiming to raise the tank to around two parts per million, then hold it there as bacteria consume it. The safety check matters: the bottle must contain no perfumes, colourings, soaps or added cleaning agents, which are disastrous in a tank. A useful test is to shake the bottle — pure ammonia solution does not foam; persistent bubbles suggest additives. Wear gloves, ventilate, never mix it with other cleaners, and keep it locked away from children and pets like any strong household chemical.
Fish food and prawn: workable, but guesswork
A pinch of fish food left to decay, or a raw prawn in a mesh bag, also releases ammonia as it rots, and this was the standard method before measured dosing became popular. It works, but you cannot know today's dose — the ammonia climbs on the decay's schedule, not yours, and overshooting slows the bacteria you are trying to grow. Decaying matter also clouds the water, smells, and can grow white mould, which is why the prawn goes in a bag you can lift out. If you use this route, test daily and remove the source when ammonia reads high rather than adding more.
Seeded media: a shortcut, not a source
Filter media, gravel or a sponge borrowed from a healthy, established tank arrives already carrying the bacteria you are growing, and it can shorten a cycle from many weeks to far fewer. But media alone adds almost no ammonia — the borrowed bacteria still need feeding, so pair seeding with one of the sources above, keep the media wet in tank water during transfer, and only borrow from a tank whose fish are visibly healthy, since media can carry disease as efficiently as it carries bacteria.
Running the cycle, whichever source you choose
Dose or add your source, test ammonia daily with a liquid kit, and wait for nitrite to appear — the sign the first bacterial colony is working. Keep topping ammonia up to your chosen level as it falls; when nitrite eventually falls back to zero while ammonia is processed within a day, and nitrate is present, the cycle is complete. That typically takes several weeks, so patience is a genuine ingredient. Finish with a large water change to bring nitrate down before stocking, and stock gradually. A multi-week routine of daily dosing and testing is easy to derail in a shared household, where the classic accident is two people dosing on the same day: KinsLe's Care Teams lets you assign each day's dose and test reading as a duty to whoever is on tank watch, timestamped when done, so the cycle log stays honest and the ammonia never gets doubled.