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How To: Cycle a Freshwater Aquarium with Dr. Tim’s

  • Marine Depot
  • Oct 23, 2020

Given the times, many of us seem to have found some extra of it, which may have us thinking about getting into new hobbies. If you have chosen to take on a the freshwater aquarium as a new hobby, got all the equipment and are ready to begin, you must first cycle the tank. But what is cycling and how do you do it? Well, before we can get into how to cycle a freshwater aquarium we must first understand why a tank should be cycled, and how the nature of it works.


Fish excrete ammonia from their gills and from their waste. Even though they produce it, ammonia is toxic and fish can’t tolerate living in water with high levels of ammonia being present. In the wild ammonia is diluted by the volume of water the fish dwells in, like a lake, or washed away by a river or stream. Yet, another way nature gets rid of ammonia, and that’s via the Nitrogen cycle.

The Nitrogen Cycle

In a perfect cycle, fish excrete ammonia, Nitrosomonas bacteria convert ammonia into nitrite, and Nitrospira bacteria convert toxic nitrite into less harmful nitrate. Nitrate is then used as fertilizer by plants, some fish eat the plants and the cycle continues – aquatic utopia. However, in an aquarium it’s not quite that perfect, because not all aquariums are planted and not all fish eat plants, so we utilize the important bits – ammonia and nitrite conversion – and just remove the end product (nitrate) via water changes.

New Tank Syndrome

Without the nitrogen cycle our fish quickly poison themselves with their own waste and perish, however, the nitrogen cycle is only possible in our aquarium with a filter and beneficial bacteria. Beneficial bacteria colonize the bio-filter media where they are supplied with oxygen, from water constantly flowing through the filter body, and ammonia, from fish waste. The colony of bacteria in your filter is a living thing, just like your fish. First you must establish that colony, then you must feed it and keep it healthy, with the return benefit of the colony converting fish waste.

Bacteria are fragile and can be accidentally removed while doing filter maintenance, killed by chlorine or chloramine in some tap water and damaged by some medicines. You have to get the colony started in the first place, and that colony needs to be sufficiently large to cope with the biological load of the fish you are putting in the tank which is the reason we need to know how to cycle the freshwater aquarium.

If little or no bacteria are present (especially in newly set up tanks,) there is an imbalance between the amount of fish waste being produced, and being converted by bacteria. New tanks showing levels of ammonia and/or nitrite have something called New Tank Syndrome. It’s the result of too many fish, too soon, and not enough bacteria present to help out. To ensure this doesn’t happen, all tanks should be cycled.


Cycling is the term we give to maturing new aquariums and filters and making them ready for fish. Every new aquarium, fresh or saltwater, should be cycled, as without it the tank will experience water quality problems early on and you may lose fish.

Freshwater aquarium cycle using hardy fish to start the nitrogen cycle
Example of outdated cycling with fish

How to begin the cycle in the aquarium first you must: set it up, aquascape it, fill it with de-chlorinated water and turn all equipment on. To properly cycle an aquarium you actually need ammonia in there for bacteria to feed on, but fish can’t tolerate it, so we fishless cycle.

Fishless Cycling

Fishless cycling is getting the tank and filter ready to break down fish waste before any fish are added to the tank. That way New Tank Syndrome can be avoided, you can add quite a few fish in a short space of time after cycling and no fish will be exposed to ammonia or harmed in the process. It’s the most humane way to cycle your tank. Here’s how to cycle the freshwater aquarium with Dr Tim’s:

You’ll need a few things to begin:

Step by step diagram of the fishless cycle of a freshwater aquarium

The Fishless Cycle Process: (from Dr Tim’s website) http://www.drtimsaquatics.com/resources/fishless-cycling

  • Day 1 – dose ammonia to 2 ppm ammonia-nitrogen [NH3-N] using our ammonium chloride (1 drop per gallon [After Nov 2016 when using DrTim’s ammonium chloride use 4 drops per gallon]) [NOTE: do not expect your test kit to exactly read 2 ppm and it is not critical to get exactly 2 ppm. The key is to not add too much ammonia].  If using DrTim’s Aquatics One & Only Live Nitrifying bacteria add it now
  • Day 2 – Measure ammonia and nitrite.
  • Day 3 – If ammonia and nitrite are below 1 ppm add more ammonia: four drops of our ammonium chloride per gallon (check the label).
  • Days 4 & 5 – Measure ammonia and nitrite.
  • Day 6 – If ammonia and nitrite are below 1 ppm add 2 ppm ammonia. Four drops of our ammonium chloride per gallon. [NOTE: since you have added the One & Only your ammonia kit will not read 2 ppm and DO NOT continue adding ammonia trying to get to 2 ppm – just add 2 ppm ammonia (4 drops per gallon of our ammonium chloride) and carry-on.
  • Days 7 & 8 – Measure ammonia and nitrite. On the first measurement day (Day 2, 4, 5, 7 or 8) that BOTH ammonia and nitrite are both below 0.5 ppm (NH3-N or NO2-N) your tank is close to being cycled.
  • Now start to measure ammonia and nitrite every day.
  • When BOTH ammonia and nitrite are below 0.2 ppm (NH3-N or NO2-N), add another 2 ppm ammonia.
  • Continue to measure every day. When you can add 2 ppm ammonia and BOTH ammonia and nitrite are below 0.2 ppm (NH3-N or NO2-N) the next day your tank is cycled – congrats! You’re done!
  • Do a partial water change and add some fish.

How to Cycle a Freshwater Aquarium Tips and Troubleshooting:

  • IMPORTANT – Do not let the ammonia OR nitrite concentration get above 5 ppm.
  • NOTE – As of November 2016 DrTim’s changed their ammonium chloride solution and you use 4 drops per gallon instead of 1 drop per gallon. Read the label on the bottle you have and follow the directions on the bottle.
  • If either ammonia or nitrite concentration get above 5 ppm, do water changes to lower the concentration.
  • Do not let the pH drop below 7. If it does, do a partial water change to bring the pH back up.
  • Do not add ammonia removers to bind the ammonia – overdosing with these products will just increase the cycling time.
  • You do not have to add ammonia everyday – the bacteria do not have to be fed every day. Adding ammonia everyday will result in a sky-high nitrite reading and slow the cycling process.
  • Is your tank bare-bottom? – if your tank does not have substrate (gravel or crushed coral) on the bottom this is called a bare-bottom tank and they take longer to cycle because there is not very much substrate for the bacteria to adhere to. If you are setting-up a quarantine tank and do not want to use a traditional substrate, consider adding some inert glass rock or marbles or some other non-calcium-based media to the tank bottom. This will help cycle the tank faster.

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