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Tips For Cycling a Tank Quickly without Fish


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Apr 3, 2020
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I read all the articles on here and elsewhere about fishless cycling and I'd done it with ammonia before on freshwater tanks. I still had a lot of questions and there were things not explained elsewhere that led my cycle to stall and take a lot longer than it could've. I figured I would share what I learned here and maybe it will help others. This info is not my mine, but is peer-reviewed science and at the bottom I'll put the 35 minute lecture you can watch if you want more info.

Here are the main points:
  • Use low salinity around 18-20 ppt (1.015sg)
    • Nitrifying bacteria survive from 10-40 but thrive at lower salinity levels.
    • At higher levels they put more effort into maintaining cell structure and reproduce much more slowly.
    • Gradually increase salinity to desired level over 2-3 days once the cycle is complete.
  • Keep Ammonia and Nitrite under 5 ppm at all times
    • You can use ammonia, shrimp, or bacteria in a bottle. Only dose to 4ppm.
    • If you use Live Sand, test before adding any additional ammonia. Decaying organics may provide all the ammonia needed.
    • If you use Ammonia make sure it has no scents and surfactants. Make sure you know the dilution so you can calculate how much to use.
    • Test often. Nitrite is the most important one to test.
    • Above 5 ppm the bacteria that process Nitrite stall. This is the reason most cyclings take longer than they could.
    • Do water changes as needed to keep levels in check.
    • You DO NOT need to keep feeding ammonia after it's processed it. The bacteria will not starve. You only add to the nitrite issue by continuing to dose.
    • Don't disrupt your substrate during water changes.
  • Eliminate Competition
    • Don't run items to remove Phosphate, Nitrate, or other micro nutrients from the water (GFO reactor, Chaeto reactor, Nitrate pads, etc).
    • Leave the lights off. They encourage algae which compete with the good bacteria.
    • Wait until the system is established to run these systems.
  • Provide media with a lot of surface area
    • Substrate is great. Bare Bottom tanks will be very slow.
    • Engineered items like blocks, balls, etc don't have much surface area relative to size and aren't great.
    • Some form of media is needed to successfully cycle.
  • Raise the temperature
    • Raise the tank temperature to 84-85.
    • Bacteria reproduce more quickly at these temps.
    • Lower temperature over 2-3 days before adding livestock.
My main takeaways are to lower salinity, raise the temp, don't dose too much, don't keep dosing, and don't run any extra equipment.

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