Saltwater Fishless Cycle Calculator
Understanding the Nitrogen Cycle
Cycling is the most critical step in setting up a successful
marine aquarium. In a closed environment, fish waste and decaying food produce Ammonia.
In an uncycled tank, this toxin builds up rapidly, burning fish gills and
damaging coral tissue.
The Goal: We are "farming" two types of
beneficial bacteria. One converts lethal Ammonia into Nitrite,
and the second converts Nitrite into Nitrate, which is
significantly less harmful and is managed via water regular changes.
PHASE 1: THE SETUP
- Setup
up: Setup your rock, sand and filter equipment. - Fill
with Saltwater: Fill your aquarium with high-quality saltwater. - Maintain
Salinity: As water evaporates, top off with RO or RODI water only.
Salt does not evaporate; adding more saltwater to top off will make the
tank too salty. - Synthetic
Seawater Additives: Using synthetic seawater, add the additional
chemicals required as per the calculator - Heat
& Light: Set your heater to 82°F (this accelerates bacteria
growth). Keep aquarium lights and UV sterilizers OFF to prevent
algae blooms. - Dose
Bacteria & Ammonia: Add your beneficial bacteria and enough pure
ammonia to reach a level between 0.25 ppm and 1 ppm – usually 1
drop per 2-3 gallons of water.
PHASE 2: MONITORING & DOSING
Test your water every 2–3 days. Your objective is to keep
the bacteria "fed" without stalling the process.
- Target
Level: Keep ammonia between 0.25 ppm and 1 ppm. If ammonia
exceeds 1ppm, do not add until it drops. - The
Nitrite (NO2) Cap: If Nitrite levels exceed 4 ppm, STOP
dosing ammonia immediately. High nitrite levels can be toxic to the
bacteria and stall your cycle. If Nitrite does not appear after 7-10 days,
bring in your water for testing, additional bacteria my be necessary. - Resuming:
Once Nitrite drops below 4 ppm, you may resume ammonia dosing. - Maintenance
Dose: If 2 weeks pass with 0 ppm Ammonia but Nitrite is still present,
add a small dose of ammonia to keep the primary bacteria colony alive.
PHASE 3: THE 24-HOUR STRESS TEST
Your tank is ready for the final check when both Ammonia
and Nitrite read 0 ppm.
- Final
Dose: Dose the tank with ammonia to reach 1 ppm. - Wait
24 Hours: Test the water again. - Validation:
If both Ammonia and Nitrite are back to 0 ppm after 24 hours, your
biological filter is fully established.
PHASE 4: PREPARING FOR LIFESTOCK
- Water
Change: Perform a 25–50% water change to export the Nitrates if
they are higher than 15ppm. - Reset
Temperature: Slowly lower the heater from 82°F to your target range
(typically 76–78°F). - Add
Life Slowly: Introduce fish and corals gradually to allow the bacteria
to adjust to the new bioload.
Pro Tips
PRO TIP: Patience is the most important
"additive" you can put in your tank. Never rush the cycle!
Weekly Cycling & Parameter Log
Log to track your progress. Consistency is key to
identifying when your cycle is "stalling" or when it’s time to
perform the final stress test.
Target Temperature during cycle: 82°F
Target Ammonia during cycle: 0.25 ppm – 1.0 ppm
Critical Limit: If Nitrite (NO2) is over 4 ppm, STOP
dosing Ammonia.
Home Stretch
The 24-Hour Stress Test
Run this only once Ammonia and Nitrite have both reached
0 ppm naturally.
- Test
Date/Time: ____________________ - Ammonia
Dose Added (to 1 ppm): [ ] Yes - Results
after 24 Hours: - Ammonia:
__________ ppm (Goal: 0) - Nitrite:
__________ ppm (Goal: 0) - Status:
[ ] PASSED (Proceed to Water Change) | [ ] FAILED (Continue
cycling)
Final Pre-Livestock Checklist
- [ ] 25–50%
Water Change performed with fresh saltwater. - [ ] Temperature
lowered from 82°F to _______ Temperature based on future livestock. - [ ] Salinity
verified at ______ (Target 1.025–1.026 sg). - [ ] Lights/UV
turned on (optional/gradual).