How to (Actually) instantly cycle an aquarium
I’ll start by immediately stating that there is in fact no such thing as an “instant” cycle- as in one that takes 0 seconds. Guilty as charged for the clickbait. However, I’m going to teach you how to properly cycle an aquarium in about as little time as scientifically possible, which in many cases is in as little as 24 hours. What IS instant is stocking- with this method you’ll be able to safely stock your tank with fish pretty much instantly after filling.
The Nitrogen Cycle (simplified)
I’ll touch on the Nitrogen Cycle at a high level, if you haven’t heard of this before I highly recommend spending a little more time researching it as it is just about the most important element of fishkeeping. The nitrogen cycle is how aquariums can keep fish in them without their waste and decaying food turning it into toxic stank water.
Very simply, the core of the entire reason aquariums (and aquatic ecosystems as a whole) can survive is due to bacteria that eats the bad stuff and poops out plant fertilizer.
Obviously thats a gross oversimplification, but that really is most of what you need to know. The other important stuff is:
Bacteria live on surfaces in your tank, like in your filter sponge or in your substrate. They don’t just float in the water.
The bacteria consumes toxic ammonia and nitrite, and release nitrate, which is mostly nontoxic and is perfect plant food.
Bacteria need oxygen to thrive- bubbles or flowing water are the best sources of oxygen.
Bacteria are hardy and won’t die easily, even if deprived of oxygen or exposed to chlorine. Don’t stress about it.
Starting a cycle
So any new aquarium needs to cycle. This means allowing the ecosystem time for this critically important bacteria to colonize the substrate, hardscape, and filter media. They need to take the clean, sterile environment and make somewhere the bacterial colonies can thrive. Once there is enough bacteria that they can consume all the ammonia in the water, the tank is considered ‘cycled’ and thus safe to start adding fish to. Adding fish before this risks the health of the fish, because any ammonia in the water can prove harmful to the fish’s health.
Traditionally, a cycle is done by setting up a tank with the filter, filling it with dechlorinated water, adding something to decompose (or just adding ammonia), and waiting a month for the bacteria to colonize.
A month?! That’s way too long! I want my fish now!
Instantly Cycling your tank
There are a million “fast cycle” products out there that offer bottled bacteria. They may somewhat work, but they’re all meant to be shelf stable and can only work so well. The bacteria needs oxygen to survive, so obviously a bottle sitting stagnant on a PetSmart shelf for 6 months isn’t going to have much helpful bacteria in it. Ask any skilled aquarist, though, and they’ll tell you that the best way to cycle a tank is to just squeeze the filter from another tank into it.
Dirty filter media from an established, cycled tank is the perfect ingredient to kickstart your tank. The gunk covering the sponge of an established tank is rich in organic matter (which the bacteria feed on), and all this organic matter is absolutely PACKED with bacteria. Not shelf-stable bacteria, but actual live bacterial colonies from a tank that’s already thriving. I just squeeze it directly into the water, the filter will pick the gunk up pretty quickly, and remember all this gunk is absolutely covered in bacterial colonies. As the new tank’s filter picks all the gunk up, it becomes covered in the exact bacteria you need for a successful cycle.
This bacteria takes 24-48 hours to colonize and fully establish itself, that’s just science and we can’t really speed that up, but they do tend to work quicker in warmer water (up to 90F, then they start to die).
While this article isn’t meant to be a way to sell you a product, we also realize that not everyone has another tank they can squeeze a filter from. If that’s the case for you, our product called FISHIT! is fresh filter gunk or pre-cycled media from our tanks that we’ll ship straight to you. You can check it out here!
When is my tank cycled?
The correct answer is when your tank has 0 ammonia and nitrite and has more than 0 nitrate- this means the bacteria are successfully converting toxins to nitrates. The best possible way to test this is with a test kit.
Over time, the trick I’ve learned is to simply look for when the tank begins to show signs of growth- both plant and algae.
While plants and algae can consume ammonia and nitrite for nutrients, they won’t really grow until the tank is cycled and is properly producing nitrite and keeping the water clean. Once this happens, you’ll pretty quickly begin seeing signs of life. Algae will begin dusting the glass or hardscape, and you’ll begin seeing new growth out the tip of the plants.
In my experience, I’ve been able to pretty confidently call the tanks cycled once I see these signs, and stop daily water changes without any issues.
So? How do I instantly cycle my tank?
Set up and fill your tank. Just get it filled with the filter running, even if you don’t have substrate or anything else yet. The longer the filter is running, the faster the tank will cycle. Be sure you dechlorinate the water, and ideally set your heater to around 80F. Bacteria grows quicker in warmer water.
Lots of air. Add a bubbler, or make sure your filter is creating tons of flow. The more agitation and surface waves, the better. This means more oxygen which means happier bacteria.
Add a lot of filter gunk from another tank. If you don’t have any, we’ll ship you gunk from our tanks! Check it out here.
Give your tank about an hour to settle, for the filter to pick up the gunk and for the temperature to equalize. It is now safe to add a few fish. Not a lot. Not hundreds. Just a few. They actually help the cycle tremendously by generating organic waste.
After 24 hours, do a major (75%) water change. A small amount of ammonia may build up, so you need to change the water daily to ensure the ammonia doesn’t harm the fish until the bacteria can catch up.
Continue doing large daily water changes until you see algae growing. Your tank is now cycled, but still keep an eye on it!
