Fish in a fish tank, whether they be goldfish, angel fish, guppies or whatever are going to produce waste in the form ammonia which needs to broken down. There are countless products on fish shop shelves that claim to establish bacteria colonies in record time but for the most part these are expensive ways and don’t really work all that well, if at all.

Primarily the nitrifying bacteria need oxygen, a food source and water movement to survive – you tell me how all this provided inside a sealed unrefrigerated bottle full of goop!

A much cheaper alternative is the fishless cycle. All you need is a couple of dollars and some patience.

What the fishless cycle does enable you to simulate waste being produced and the establishment of the bacteria to process it in a controlled environment.

Aside from having this control the biggest advantage is that fish aren’t involved in the cycling process. When you are finished cycling using this method any fish you do add to your tank aren’t exposed to toxic water levels as a result of cycling.

Last week I posted about the importance of cycling your fish tank before adding any fish. Primarily what we are doing it establishing a nitrogen cycle which is in equilibrium with the waste your fish are going to produce.

This weekend I’m going to continue the ‘cycling you aquarium’ theme and show you just how easy it is to cycle your aquarium.

Here’s a list of things you will need:

• 1 bottle of clear ammonia (not cloudy, soaped or with any added detergents)
• 1 water test kit (of importance are ph, ammonia, nitrITE and to a lesser extent nitrATE)
• millimeter measuring container


The first thing you need to do is to set everything up like you would if you were going to add fish. If you’re unsure of what to connect up or what’s the best order to do everything in I’ve previously written a guide on setting up a goldfish tank. Note that even if you’re not keeping goldfish many of the steps are the same and it should be of some use.

Lighting and bubblers can be turned off as all we need is water flow from the filter. If you are using a heater set the temperature to 80 deg F (27 deg C), this is roughly the optimum temperature to promote optimal bacteria growth.




1. Creating an ammonia source

The main objective of fishless cycling is to create a large enough colony of bacteria inside your filter to cope with the fish as you add them. The good news is this is mostly a passive process.

What we want to do is raise the ammonia level in your fish tank to 1ppm (this is where the aquarium test kit comes in handy). Start by adding a few ml of ammonia and take a reading of the water with your test kit.

Unfortunately there’s no blanket rule as to how much ammonia will achieve a reading of 5ppm as manufacturers vary the ammonia to water ratio and obviously it’s all relative to the size of the aquarium you are cycling.

Once you’ve reached a reading of 1ppm with your water test kit record the amount of ammonia used. Using some basic maths, then proceed to add enough ammonia to achieve a reading of 5ppm.

Don’t worry if you go over slightly, it’s not going to have a negative effect. If you massively go over by accident it might be a good idea to empty out half the tank, refill it with clean water, take another reading and start again.

The reason for this is too much ammonia initially can hamper the growth of the processing bacteria. I’m not sure why it happens but all we need to know is it does.




2. Monitoring the ammonia level over the next few days

Initially it’s probably going to take a few days to a week for your ammonia processing bacteria to kick in and start eating up the ammonia. What I’d advise doing is leave the tank alone for three days and then take a reading.

What you are looking for here is a drop in the ammonia level and an accompanying rise in the Nitrite level.

Remember this can take a week or so to start happening so don’t panic if after 3 days ammonia is still sitting at 5ppm. If after a week ammonia hasn’t budged there might be something prohibiting bacteria growth.

Here’s a brief checklist:

• Did you fill the tank with treated water?
• Is the filter running?
• Is your ammonia source absolutely free of chemicals and soaps? A quick check is to shake up the bottle, if it bubbles at all then it’s no good and you’ll have to start again with a different ammonia source. Note large clear bubbles that quickly disappear when you stop shaking should be ok.




3. Topping up your ammonia and watching for a nitrite spike

As ammonia is processed you want to top it up again. Initially it will take a few days for Ammonia to drop to 0-1 but after a while your ammonia consuming bacteria should be able to process 5ppm daily.

To start with though I’d wait for it to gradually hit 1ppm and then top back up to 5. Eventually your ammonia will be dropping to 0 daily and you’ll be topping up to 5ppm but this is towards the end of the cycle.

In addition to ammonia being processed you’ll also notice your nitrITEs start to spike. This is because nitrite is the by product of your ammonia consuming bacteria. It spikes intially because the nitrite eating bacteria needs a little while to establish themselves.




4. Watching Nitrite drop and the production of Nitrates

The production of nitrATEs signals you are almost done cycling your tank and should co-incide with a reduction of nitrites in your tank. At this stage don’t worry about what level the nitrates get to too much. If you’ve got plants they’ll love the extra food but insanely high levels (100+) aren’t going to hurt the bacteria we’re cultivating.




5. Knowing when your tank has finished cycling

Eventually your tank will be able to process 5ppm of ammonia daily, have a 0 nitrite reading, a high level of nitrates and possibly insane algae/plant growth!

Congratulations, at this point your tank has finished cycling.




6. Adding fish

It’s important to keep feeding your bacteria until you’re ready to add fish to your tank. For example if your tank finishes cycling during the week but you aren’t going to go buy some fish till the weekend, don’t starve your bacteria by not feeding them as they will die off and you could undo your cycle.

On the day you’re buying fish be sure to empty out the fish tank and fill it with clean water. Scrub any algae that has accumulated (most likely brown diatoms) inside the tank or on the glass and perhaps give the filter a quick clean. Your filter shouldn’t be too dirty given it has been processing liquid waste only but it doesn’t hurt to check if it needs a going over.

Once this is done fill the tank with nice clean treated water and go buy your fish. The good news is because you’ve been adding 5ppm of ammonia daily, you’re pretty much right to add the total number of fish you plan to keep without worrying about a mini cycle occurring.

A mini cycle occurs when your bioload increases suddenly and your existing bacteria have to multiple to keep up resulting in a possible small ammonia and nitrite spike.

When adding your fish be sure not to overstock your tank as this will lead to poor water quality even if you’re tank has cycled. If your bioload exceeds your filters capability then your water is going to get toxic fast.




Some additional notes


If your cycle stalls suddenly

If your cycle inexplicably stalls at any point one thing to check is the ph. Bacteria processing waste eats into the carbonate hardness of water and if this hardness level gets too low the ph can crash and then stall your bacteria.

I went a week with my cycle suddenly stalling before hitting the internet for answers.

If the ph has dropped to <6 add some baking soda to bring the kh back up and stabilise the ph again. If your tap water is prone to ph crashing and is soft (lack of kh) then it’s worth adding a stocking of crushed coral or crushed oyster shell to one of your filter compartments.

This will automatically regulate the kh (the shells will dissolve slowly as needed) and works far better then any commercial ph stabiliser.


Clear ammonia isn’t available in my country!

Living in Australia this was a problem for me as pure ammonia wasn’t commercially available. I did manage to track down one chemical supplier who wanted to sell me 1 litre for $25 but knowing that a bottle of ammonia sold in the US was a few bucks I politely declined.

Luckily you can still use the fishless cycle if ammonia isn’t available in your country. To produce ammonia simply purchase 2-3 raw prawns and tie them up into a stocking and place the stocking inside your tank.

Note when buying the prawns and stocking you might want to bring a female friend along. I felt like the biggest pervert walking around Coles carrying the cheapest pair of stockings I could find and a deli package of 3 prawns. More so when I rocked up to the register to pay.

‘Hi these are for my fish tank.’

‘…suuuuure they are.’

After a few days the prawns will start to rot (and smell a little) and the stocking will get covered in white fungus crap. This will eventually start to produce ammonia and start the cycle off. It’s a bit more imprecise then the clear ammonia method but should produce more then enough ammonia to complete a fishless cycle.


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Related posts that might interest you:

1. Why do I need to cycle my goldfish tank?
2. Choosing a filter for your Goldfish Aquarium
3. The Walstad Aquarium and Goldfish: My conclusions
4. Walstad Goldfish Tank Update August 2009
5. Setting up a Goldfish Aquarium Tank Guide