Fishless Filter Cycle

  • #1
I have learned so much here about tank cycling, I wanted to share back my own recent (ongoing) cycling adventures with the hope that this little log will help someone else.

A little background:
I am in my first year of fish keeping, and building my 3rd tank, a 22 gallon long planted hi tech tank. The tank is currently hardscaped with rock and wood built on egg crate, but I am not yet ready to plant, and there is no substrate in place yet. While planning and buying plants, I decided to get a jump and attempt to cycle my filter, an Oase biomaster 350 thermo. This filter is a beast, and rated well over the size of this tank, so I am pretty excited to see what it can do.

I loaded the filter with about 2 kg of Biohome media, filled the tank with dechlorinated water and went for a fishless cycle. I am not in a real hurry because I am still working out the planting plan, and decided to document things as they went along. Here is what is happening so far:

Day 1
Tap water parameters:
Ammonia from the tap reads 0.25
Nitrites and Nitrates are 0
pH 7.0
KH 2-3
GH 3-4
TDS 85
Temp: 82 F
Two air stones running 24/7
Lights off
CO2 off
No substrate, no plants
Dechlorinator is API tap water conditioner
Testing is API

I am dealing with pretty soft water here in the PNW of the US. Chloramines leave trace ammonia, and not allot of minerals.

I had no ammonia on hand to start, so added 1/4 tsp of fish food to start. Then, 5 ml of Stability daily for about a week. This produced nothing measurable.

Day 5
Got some Fritz Fishless Fuel in the mail and dosed the tank to 2 ppm ammonia, still adding 5 ml Stability daily. Still nothing for about another week.

Day 10
Squeezed a filter sponge from a small established tank into the water column, and seeded the filter trays with some gravel and filter media from another established tank. My other tanks are small so not much seeded media was available. Continued daily dosing 5 ml Stability and occasionally adding a tiny pinch of fish food to the water column (every few days).

Day 17
13 days after dosing ammonia to 2 ppm with the Fritz Fuel, we have some action with an ammonia reading of 0.25 ppm! I thought this was pretty cool, so I ran a panel:

Ammonia: 0.25 ppm
Nitrites 2.0 ppm
Nitrate: 5.0 ppm
Phosphate: 0.25 ppm
PH: 7.0
KH: 3 dKH
GH: 4 dGH
TDS: 121 ppm
Temperature: 85 Degrees F

Looks like this cycle is on it’s way after 13 days of Ammonia and Stability. I was feeling pretty cavalier and decided to up the ammonia, and dosed to 3ppm. Mistake. This led directly to my pH crashing the next day. It might have happened anyway, but I think dosing 3 ppm was an error.

Day 18:
Ammonia: 2 ppm
Nitrite: 2 ppm
Nitrate: 5.0 ppm
KH: 1 dKH
PH: 6.0

Because I read this forum, I knew that this pH crash was a possibility and knew what to do:
- put a handful of crushed coral into the filter to get my water buffer back (nitrification is an acidic process that eats KH and lowers pH, slowing the cycle)
- performed an 80% water change to remineralize the water column
- lowered the temperature to 82 F
- added 5 ml of Stability

Retesting immediately after this, Ammonia reads 1.5 ppm, KH still at 1, and pH bounced back right away to 6.8.

Day 19
By morning, pH had recovered to 7.2, KH 3, and GH to 6. Ammonia was down to 0.25, so my assumption is a cycle stall was averted. My takeaway here is I got greedy by dosing Ammonia to 3 ppm too soon with such a lean buffer (KH), and I avoided a bullet here.

I dosed ammonia to 1 ppm and decided to maintain that dose till nitrites measure zero.

Day 21
Ah, nitrites. I realized that I have been misreading the nitrite tests, and they have likely been off the chart instead of the 2 ppm I thought I was reading this whole time. Those shades of purple are hard to distinguish! Again, thanks to this forum I learned about diluted testing and ran a batch of diluted tests for nitrites:

1:0 - off chart
1:1 - off chart
1:4 - off chart
1:5 - off chart
1:9 - 0.5 ppm (confirmed with re-test)
1:19 - 0.0 ppm

0.5 ppm x 10 = 5.0 ppm nitrates. I know this is not entirely (remotely?) accurate but it is something to work with.

I decide to do an 80% water change and got the nitrites down to 2 ppm, and plan to maintain ammonia dosing at 1ppm till nitrites process to zero.

Day 23 (TODAY)
Two days later, patience pays off and my nitrite test is sky blue zero, my ammonia is bright yellow zero, and my nitrates are slowly climbing at 30 ppm. I am stoked that this cycle is working! I now believe that I just need to slowly grow my fledgling colony by gradually dosing more ammonia and only upping the dose as nitrites clear.

I assume that my nitrAtes will continue to climb, and I am not sure how high nitrate levels will effect my cycle. My current plan is to do water changes once nitrates read bright red, or > 80 - 160 ppm, and keep them in check throughout the rest of this cycle with water changes. Does this sound reasonable? Does anyone know how climbing nitrates will effect the cycle?

Thanks for reading, I hope this information is helpful to someone going through the same thing.


  • #2
climbing nitrates are signalling the end of the cycle, just do small to medium water changes to get them down, but if you ant to be sure, do a water change, then add ammo. and if it registers, then wait 24 hours and if its gone, then your tank is cycled

  • #3
Perfect. Thank you for posting this. I am sure your experience is going to help others understand how important it is to continually test and even do water changes during a fishless cycle as needed. By catching the pH drop and replenishing the minerals as quickly as you did you prevented a slowdown in the process.

Starting low and gradually building up the bacteria by gradually increasing the amount of ammonia being added is basically what happens when others slowly increase the stock in a tank so in my humble opinion what you are doing is the best way to do it. Allowing the bacteria to catch up with the amount of ammonia being added keeps our bacteria from being overwhelmed.

The fact that you also added fish food along with the bottled ammonia is something I recommend for all fishless cycles. I think it helps build a stronger more natural cycle and should prevent issues once fish are added.

I think nitrates would have to get very high before causing issues but I will recommend you try to keep them down to 40 or so with water changes. Not only will the water changes get the nitrates down but will also replace minerals.
  • Thread Starter
  • #4
Thank you for the responses. Mattgirl, I added the occasional pinch of fish food to suppliment the ammonia doses on your advice - the theory makes sense to me.

I agree that slowly building the colony by starting with low doses of ammonia is a good idea. Dr. Tim agrees:

“Bacteria … do not need to eat every day to survive. Because the ammonia-oxidizing bacteria work faster than the nitrite-oxidizing bacteria the ammonia will read zero sooner than the nitrite will read zero.
1) do not add ammonia if either ammonia or nitrite is above 5 mg/L
2) only add a maximum of 4 drops per gallon do not continue to add ammonia until you get a reading of 2 ppm or else you risk overdosing the system with ammonia”

This cycle has so far been an interesting and satisfying learning experiment. I am certain it would not be the same experience if I were doing a “Fish in the tank” cycle. If there were live critter involved, I would be seriously stressed and probably rush and make more mistakes. More advanced aquarists probably have no issues doing fish-in cycles, but for the beginner there is so much that can go wrong at the expense of the animals. I highly recommend fishless cycling for the beginner.

Still in the unknown column, I am not sure what will happen when I add the substrate (ADA Amazonia). I know this product will leach a fair bit of ammonia into the water - wondering how much and how my young colony will handle it. There will be no fish involved yet, so whatever happens, it’s ok. I will continue to observe, test and report progress.

Thank you again to this amazing community!

Day 25
Two days after dosing ammonia to 2 ppm, ammonia and nitrites have cleared to zero, and nitrates are reading 80+ ppm. pH is stable at 7.2. I perform a 75% water change to clear out some nitrate, and dose the tank to 2 ppm. My plan is to maintain dosing at 2 ppm till ammonia and nitrites zero out within 24 hrs. Will test tomorrow.

I am excited this cycle appears to be working! Thank you everyone that has contributed to this forum, your shared knowledge has been a tremendous help.
  • #5
Since you will be gradually increasing the amount of ammonia you are adding I have to think you will have grown enough bacteria by the time you add the substrate to handle the amount of ammonia it is going to produce. 'specially if you eventually get it up to where it is processing 3 or 4ppm ammonia.

I do know some folks including, it seems, Dr. Tim recommends letting the nitrites zero out before adding more ammonia. That will work but I look at it a bit different. I recommend adding ammonia each time it drops down to or very close to zero even though we are still seeing nitrites. Either way will work but I like to see a steady supply of ammonia added and nitrites being produced. Eventually we will have grown enough nitrite eating bacteria to zero it out and at that point we will have a strong colony of both ammonia and nitrite eating bacteria.

Adding more ammonia each time it goes down is much like it would be if we were dong a fish in cycle. Fish are adding a constant supply of ammonia. In the case of a fish less cycle we can grow a very strong cycle by controlling the amount of ammonia the tank will process. Once we have enough bacteria to process the original amount straight through to nitrates we gradually increase the amount of ammonia we add and both ammonia and nitrite eating bacteria will very quickly multiply to clear it out.

If it was processing 2ppm ammonia increase it to 2.5. Once a tank can process 2ppm ammonia it will very quickly grow enough bacteria to process 2.5 I wouldn't even expect to see a nitrite spike with that slight increase in ammonia. If the ammonia is gone within 24 hours and we see no nitrites we can then add 3ppm. Continue upping the amount until you are sure you have enough bacteria to handle the planned bio-load of the tank.

Saying you should not see any nitrites is only if we have kept feeding the ammonia eating bacteria each time it dropped to zero and allowed the nitrite eating bacteria a chance to grow in great numbers. If we stop feeding the AEB long enough for the nitrites to zero out each time the NEB isn't going to be as strong as it can be. It is true that the nitrites may get to what some consider uncomfortable numbers but that isn't a problem when fishless cycling.
  • Thread Starter
  • #6
Thanks for the reply mattgirl - you make good points and I appreciate your expertise. I got into fish keeping because I thought fish would be an easy pet to start with my children, but I am finding that fish are the most complicated animals I have ever had to keep! I feel fortunate to be able to mess with this 20 gallon set up and learn a little along the way.
  • #7
climbing nitrates are signalling the end of the cycle

So we want to see high Nitrates?
What about early in the tank's life?

I just posted a thread trying to understand this.
  • #8
Thanks for the reply mattgirl - you make good points and I appreciate your expertise. I got into fish keeping because I thought fish would be an easy pet to start with my children, but I am finding that fish are the most complicated animals I have ever had to keep! I feel fortunate to be able to mess with this 20 gallon set up and learn a little along the way.
Absolutely agreed! So many people mistake fish as being an "easy starter pet"...that couldn't be farther from the truth. It's like saying if you have a farm, the first animal you should get is a pig. Sure, pigs'll eat anything but they're not as easy as you'd think once you get into the territorial issues, digging, vet costs and endless food supply!

In my opinion, the easiest starter pet overall is a tarantula. Hamsters are easy-ish but you have to worry about proper nutrition, substrate depth, vet care costs, massive enclosures and large enough wheels. They're not cheap or "easy".

Don't even mention goldfish or hermit crabs...
  • #9
So we want to see high Nitrates?
Yes, unless you have plants or algae growing, in which case you may not be able to see nitrate get high given both consumes nitrate.
What about early in the tank's life?
Can you clarify what you mean by 'early in the tank's life? Like during the cycling process, or the period just after cycling? Or just like early on when a tank is just set up in general?

I know you have another thread but it was unclear what everything was, so figured I'd respond to you here.

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