Cycling an aquarium can be free or cost up to $30 - here's the spectrum. $0 - seeded media (best + free): from a friend with an established tank, take a section of mature filter sponge, a cup of substrate, or some "ugly" rocks. Place in your filter and run for 7-14 days. Bacteria transfer is immediate. $5 - dose with fish food: drop 5-7 flake food pellets into the tank weekly. They decompose into ammonia. Tank cycles in 4-6 weeks. Doesn't kill any animals. $15 - bottled bacteria: Dr. Tim's One and Only or FritzZyme 7 contain real Nitrosomonas + Nitrospira. Combined with daily ammonia dosing (Dr. Tim's ammonium chloride or Janitorial Strength Ammonia from Ace Hardware), cycles in 1-2 weeks. $30 - full kit: bottled bacteria + ammonium chloride + API Master test kit. Most reliable + measurable. Avoid wasting money on: "cycle starter" products that aren't Nitrospira-based (Stress Zyme, Cycle, etc. - many lack the right bacteria). Saltwater specifics: live rock cycles in 1-2 weeks for $4-6 per pound. Dry rock + bottled bacteria + Dr. Tim's for marine = $40-50 setup but cheaper long-term than live rock.
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