The 7 cycling mistakes that crash new aquariums. How to do a fishless cycle correctly + when to add fish.
The #1 cause of "my fish died after a week" is ammonia poisoning from an uncycled tank. Cycle takes 2-6 weeks. ALWAYS verify with a test kit that ammonia + nitrite both convert to 0 within 24 hours of dosing 2 ppm ammonia before adding fish.
Household ammonia often contains surfactants, fragrances, and detergents that kill bacteria. Use ONLY pure ammonium hydroxide or chloride. Brands: Dr. Tim's Ammonium Chloride, Ace Hardware Janitorial Ammonia (verify label is pure).
New filter floss is fine but biological media (ceramic rings, bio-balls, sponges) holds the bacterial colony. Replace mechanical only; never replace biological media all at once.
Chlorine + chloramine kill the cycling bacteria. ALWAYS use Prime/dechlorinator OR RODI water for water changes during and after cycling.
"It's probably done" is the most expensive guess in the hobby. Test ammonia + nitrite + nitrate every 3 days during cycling. Only add fish when both ammonia + nitrite read 0 within 24 hours of a 2 ppm ammonia dose.
Fishless cycle = fishless. If you want to do a fish-in cycle, ONLY use a few hardy guppies/danios + dose Prime daily + small water changes weekly. Most fish die during fish-in cycles.
After cycling, nitrate accumulates to 30-80 ppm. Do a 50% water change BEFORE adding livestock to drop nitrate to safe levels (under 20 ppm).
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