How Long to Cycle a Tank With Seeded Media


Cycling a tank is the process of establishing the beneficial bacteria colonies that are needed for biological filtration. These bacteria consume ammonia (fish pie) and nitrite (fish poop), converting them to nitrate, which our plants then use for growth. The primary goal of cycling a new aquarium is to succeed with fish keeping without purchasing pricey chemical additives or liquid bacterial cultures from your local fish store.

How Long to Cycle a Tank With Seeded Media

Seeded media in a tank is basically the glass beads/rocks that act as a seed for live plants and algae growth. This media helps accelerate the cycle time by providing more food to the population of Nitrosomonas, which, in turn, helps deplete Ammonia at a much higher rate than just using, say, good ol’ tap water.

However, it will not decrease the duration from 10-14 days altogether but rather reduce your waiting period to see ammonia dropping from “0”. So, instead of waiting 14 days with an empty tank, one can have a full ammonia drop within 7-10 days if you are lucky. In this article, I will discuss “how long to cycle a tank with seeded media.” So, let us get started.

Reasons For Using Seeded Media to Cycle a Tank

  • Cycling a tank with seeded media is the fastest way to cycle a tank
  • If you have snails, then using seeding media will prevent them from eating live bacteria in your filter
  • You can use cheap, non-nutritious food as a source of ammonia for cycling fishless or with existing fish if you choose this route
  • No live fish is required, and therefore, no worries about disease/mortality associated with adding new livestock
  • It’s cheaper than buying a huge dose (30%-50%) of ammonia right off the bat when starting your first fishless cycle. It’ll require fewer daily or bi-weekly dosing because there is already an abundance of oxygen-promoting bacteria present in the form of nitrifying bacteria/Nitrosomonas. All-in-all, Seeded media is ideal when getting started cycling smaller tanks of under 20 gallons, and you’re using food as a source of ammonia to be consumed by the beneficial bacteria in your filter.

However, for larger tanks that need more dense colonies of nitrifiers, high percentage ammonia (30%-50%) fishless cycle is necessary for a faster startup; therefore, seeded media may not be the best option depending on tank size and level of patience required. Nevertheless, the steps below are created to use seeded media in your tank.

Larger Tanks That Need More Dense Colonies

How Long to Cycle a Tank With Seeded Media?

The primary factor involved in how many days it will take to cycle a tank is the number, quality, and type of bacteria present in your new aquarium.

This is why you must always wait at least 7-14 days from when you place new fish into your cycling tank before you add any more fish (or add any other source of ammonia), or your bacterial colony may not be able to handle it.

If this happens, ammonia levels will spike again (because no bacteria are left to process the extra ammonia), and your fish will most likely die. You can avoid this by simply waiting for 14 days after setting up your tank to put any fish in it. Of course, if you’re like me, you’ll probably do something else instead (like watching paint dry).

If you are going to add more fish before the tank is cycled, I suggest picking fish with a much higher tolerance for high ammonia levels so they can survive while your bacteria are getting established. For instance, some people will cycle their tanks with daphnia and/or small guppies because these organisms produce very little ammonia and will thus slowly increase the level in your tank over time.

Add More Fish Before Cycled

However, most community fish should not be added until the tank has been cycled because they tend to die easily from high ammonia or nitrite levels. Suppose you start cycling your tank with live plants (which consume ammonia). In that case, you won’t need to worry about adding any extra source of ammonia for the first couple of weeks while your bacteria colony is getting established.

Another essential part of cycling a new aquarium is feeding the fish only small amounts (once or twice a day) and avoiding overfeeding (which most people do). Overfeeding will cause the ammonia level in the tank to rise much faster than normal because more food will decompose into ammonia when it rots in your tank instead of being eaten by your fish.

The higher ammonia levels will poison some of your nitrifying bacteria, allowing other types of toxic bacteria to start growing that may kill your fish. This is why it’s so important not to overfeed during the cycling process.

Over time, you’ll learn how much food each of your individual fish needs, and you’ll be able to tell when they’re satisfied by observing how much of their food they eat.

As a general rule, your fish should have plenty of hungry days here and there rather than lots of well-fed days all the time. The one exception is if you are worried about having a large number of skinny fish that might not stay alive in your tank due to competitive pressures from the other fish (in which case, by all means, overfeed).

Precautions While Using Seeded Media to Cycle a Tank

  • Do not add fish to the tank until it has been cycled.
  • Be careful what you feed your fish while in the tank during its cycling phase. Make sure that the food contains no ammonia or nitrite.
  • Wash your hands before maintaining or servicing an aquarium containing seeded media, as even traces of harmful chemicals can kill beneficial bacteria in a tank.Wash Your Hands
  • Do not clean out or disturb any tank part except for cleaning glass and rinsing gravel. This could disrupt the vital bacterial mat necessary to cycle an aquarium fully.
  • Be sure to add dechlorinating and conditioner agents when using treated tap water or setting up aquariums. Tap water contains chlorine, chloramines, and other chemicals that can kill a tank’s beneficial bacteria.
  • Remove fish from the tank for 10–15 minutes before vacuum cleaning the bottom of the tank and remove excess detritus materials such as decaying plant matter from gravel with your hands instead of removing them by the bucket. The difference between 15 minutes and 1 hour could mean life or death for your beneficial bacteria colony.


I hope this article has been beneficial for determining how long to cycle a tank with seeded media. Thank you, and have a nice day!

Jennifer Branett
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