10 Gallon Tank Cycling Step by Step Guide
Skip cycling on a 10 gallon tank and you are gambling with the lives of whatever you stock. This 10 gallon cycling step by step guide takes you from a freshly filled 38-litre tank to a stable biofilter ready for fish, using the fishless ammonia method that has become standard practice at Gensou Aquascaping, 5 Everton Park. A 10 gallon measures 20 by 10 by 12 inches (51 by 25 by 30 cm), holds 38 L, and cycles faster than larger tanks simply because small water volumes shift test readings quickly — which makes the process easier to follow.
What Cycling Actually Does
Cycling establishes two nitrifying bacteria colonies in your filter and substrate. Nitrosomonas converts ammonia to nitrite, and Nitrobacter (plus Nitrospira) converts nitrite to the far less toxic nitrate. Without these colonies, fish waste accumulates as ammonia within 48 hours and kills stock. The goal is to grow the bacteria before you add fish. Our nitrogen cycle for beginners article covers the theory.
What You Need Before Starting
Gather pure ammonia (Dr Tim’s Ammonium Chloride from Iwarna at $22, or unscented Ace Hardware household ammonia at $8), an API Freshwater Master Test Kit ($55), a bottle of Seachem Stability or Dr Tim’s One & Only ($25) for bacterial seed, and dechlorinator like Seachem Prime ($14). Budget $110 to $130 for the cycling kit. PUB tap water cycling works fine once chloramine is neutralised.
Day 1: Fill, Dechlorinate, Seed
Fill the tank with tap water dosed with Prime at 1 drop per 4 litres (roughly 10 drops for 38 L). Start the filter and heater; target 28 to 30°C to accelerate bacterial growth. Singapore ambient hits this naturally, so heaters are usually unnecessary. Add the full recommended dose of Seachem Stability on day one, day two and day seven. Introduce ammonia to reach 4 ppm — about 4 ml of Dr Tim’s per 38 L. Test ammonia immediately to confirm 4 ppm.
Days 2–7: Ammonia Phase
Test daily for ammonia and nitrite. Ammonia should remain at 4 ppm; nitrite should read zero. If ammonia drops below 2 ppm before day 10, dose back up to 4 ppm immediately — starving the bacteria sets you back a week. Around day 5 to 7 you will see the first nitrite reading, which means Nitrosomonas is working. PUB tap water at 29°C typically shows nitrite by day 6, three days faster than temperate-climate tanks.
Long-Tail Variant: 10 Gallon Cycling Step by Step Guide Using Seeded Filter Media
If you can beg a handful of filter media from a running tank — a used sponge, a bag of ceramic rings, or even a pinch of substrate — the cycle compresses from 4 weeks to 10 to 14 days. Drop the borrowed media into your new filter’s chamber on day one, add ammonia as normal, and watch nitrite appear within 48 hours. Shops at C328 Clementi and Iwarna Aquafarm occasionally sell “mature” sponge filters in the $15 range — worth every dollar. See how to cycle a sponge filter fast.
Days 8–21: Nitrite Phase
Once nitrite appears, continue daily ammonia dosing to 2 to 3 ppm if readings drop. Nitrite will spike — expect 2 to 5 ppm in the peak, which is normal and harmless to the unstocked tank. Nitrate begins to show on API test card at a yellow-to-orange transition, climbing steadily from day 10. The slowest part of cycling is growing Nitrobacter / Nitrospira; this is where most cycles stall and where bottled bacteria help. The aquarium cycling timeline shows typical test readings by day.
Days 22–28: Nitrite Drops, Cycle Completes
Around day 20 to 25 you should see nitrite fall from its peak towards zero within 24 hours of an ammonia addition. Dose ammonia to 2 ppm in the evening; test the following evening. If both ammonia and nitrite read zero and nitrate reads 10 to 40 ppm, your cycle is complete. Do one 50 percent water change to drop nitrate below 20 ppm, wait 12 hours, and you are ready to stock.
Plants Accelerate Everything
A heavily planted 10 gallon with fast growers like hornwort, water sprite and Limnophila absorbs ammonia directly through leaves and roots. This silent plant uptake can shorten cycling by 30 to 40 percent and in some cases produces a cycle without a single measurable nitrite spike. If you plant from day one, dose ammonia more conservatively (2 ppm instead of 4 ppm) because plants will process much of it. See aquarium cycling with plants.
Why Singapore Ambient Helps
Nitrifying bacteria double fastest at 28 to 30°C, exactly our HDB ambient. Temperate-climate guides quote 4 to 6 week cycle times; Singapore tanks cycle in 2 to 4 weeks without heaters, purely because kitchen ambient sits in the optimal growth zone. This is one of the few fishkeeping areas where our climate works in our favour.
Signs of a Stalled Cycle
If ammonia stays at 4 ppm past day 14 with no nitrite appearing, your pH has likely crashed below 6.5 (ammonia oxidisers stall) or chloramine wasn’t fully neutralised. Dose a double shot of Prime, check pH, and consider adding more Stability. Cycles also stall from using antibacterial products or washing filter media in tap water. See nitrogen cycle troubleshooting.
First Stocking and Ongoing Maintenance
Add fish in stages, not all at once. Start with 3 to 4 hardy species (amano shrimp or a small rasbora shoal) week one, add 4 to 5 more after a fortnight once ammonia stays at zero, and finish with any feature fish by week four. This phased introduction gives the biofilter time to scale bacteria population to match bioload — see the stocking order planner. Maintenance thereafter is weekly 30 percent water changes with dechlorinated tap water to keep nitrate under 20 ppm long-term. Squeeze filter media monthly in old tank water only, never tap water. Test ammonia and nitrite weekly for the first three months; after that, stable tanks rarely need ammonia testing unless something visibly changes.
Related Reading
emilynakatani
Still Have Questions About Your Tank?
Drop by Gensou Aquascaping — most walk-in questions get answered in under 10 minutes by someone who has set up hundreds of tanks.
5 Everton Park #01-34B, Singapore 080005 · Open daily 11am – 8pm
