I have some questions regarding fishless cycling of a 65L tank I have set up 2 days ago. Please bear with me.

I set up the tank with tap water, and added an appropriate amount of Seachem Prime to dechloronate. The tank has a HOB filter and a set of LED lights (for full details of tank set, see here.

The tank has some amazon frogbit and hornwort floating around, as well as tiny amounts of duckweed. I accidentally also added in a tiny dash of liquid fertiliser NOT designed for an aquarium (see here). Will this fertiliser harm any fish I put in there in the future? Will it affect cycling? Also, will the ingredient "biuret" harm the fish? I tried looking this up to little success; all I know is biuret is a condensation of urea or something.

I live in Australia, and cannot add ammonia into the tank. Instead I popped in some goldfish pellets and cichlid pellets which I had lying around from years ago. The idea is for this to decompose and produce ammonia, to start the nitrogen cycle.

Today I went to the pet store and was advised that I need to add Seachem Stability for my cycle to go well. I have not done this. Can anyone advise me if Stability is required or beneficial for cycling?

Also, I did a quick ammonia, nitrite, and nitrate test today with an API 5 in 1 kit. All showed values of zero (I even re-tested the nitrate in case I didn't shake the bottle enough, and still zero).

Can anyone tell me why all my values are zero? I thought that nitrates should not be zero after a cycled tank. Is my tank cycled? It's only been 2 days. If my tank isn't cycled, why is my ammonia and nitrite reading zero? Are my plants sucking up all the ammonia?

One last thing is that the water of my aquarium is cloudy. Is this bacterial bloom? Algae? I've also noticed on the fish pellets a white halo of something growing on it. Is this fungus?

I've never cycled a fish tank before, and I really hope to get it right this time. I also have NOT conducted any water changes since setting up the tank. Please advise if this is appropriate.

To sum up:

  • Will a urea-based fertiliser not made for aquatic use harm fish? Will the tank cycling properly with this? Will biuret harm fish?
  • Do I need Seachem Stability to cycle a tank or not?
  • Why is my tank showing ammonia 0, nitrite 0, nitrate 0? Does this have to do with my plants? Is my tank cycled?'
  • Does my tank have bacterial bloom or something else?
  • Do I need to worry about white fuzz around my decomposing fish food?
  • Do I need to do water changes for this fishless but slightly planted cycle?

I can't add images at this time for some reason and Stack Exchange isn't letting me add more links which is frustrating. I do have photos to show though if anyone will find them useful!

P.S. I'm planning on putting a betta in there and possibly some tank mates once things are established.

  • 2
    dont use nitrogen (urea) fertiliser in a fish tank(in a plant only tank it is ok to use it but you risk unwanted algae).the fertiliser for fish tanks do not contain nitrate as the fish suply more than the plants need of nitrate(this is why we do water changes to get rid of exsess nitrate and waste). Nov 22, 2017 at 10:39

4 Answers 4


Just leave it for a month or so. More than likely you will get some decaying material from the plants which will naturally kick-start the cycle. If you put food in there at all, it will absolutely kick-start a cycle as well, just don't add any more, you'll foul up the water too much at this point.

Some observations, I'm assuming you're using the test strips. These things are notoriously inaccurate, I've literally seen them never register anything. Take any measurement with test strips with a grain of salt.

Second, you don't need anything more than prime. Seachem Stability is a completely optional product. It "can" reduce the time it takes to cycle, but you don't need it at all in your situation since you're not adding fish yet. Plants will be fine through a cycle as long as they have enough light.

Cloudy water is most likely a bacterial bloom at this point. It's not uncommon during a cycle. If it gets really bad, do a partial water change. This should clear up as the nitrifying bacteria establish. The caveat to this statement is that if you put way too many nutrients into the tank, you may need to take care of it with water changes and mechanical filtration.

Most likely fungi or bacteria around the pellets. Don't add more. Take them out if it starts spreading too much.

Finally, don't add fertilizers or anything else to the tank right now. I don't recommend fertilizing at all for the first few months. After the initial cycle, the tank still goes through a number of biological processes which will typically include several stages of algae. The more you mess with the tank at this point, the easier it is to get unbalanced chemistry which leads to more algae and other problems. Work on getting the tank on a routine water change schedule once the cycle is complete. Once you have a stable environment, then consider fertilizers if needed. But you really want the tank established and stable before considering them.

As far as fertilizers in general, in a closed system like an aquarium, you have to find the balance between light, nutrients, and CO2. If any of these are imbalanced, you'll likely have algae issues. If you aren't dosing a CO2 product or using a CO2 system, I would be very cautious with fertilizers. Natural CO2 concentration in aquariums is typically very low, so plants can only consume so many nutrients in the tank. It's extremely easy to overload the system with nutrients using fertilizers in a low light or tank without added CO2. Anyway, get the tank stable first, worry about fertilizers later.

  • 1
    I'm not using test strips; it's the bottles and test tubes.
    – Ribika
    Oct 5, 2017 at 2:43

To address your concern about the non-aquarium fertilizer, once the tank has cycled, do a 50% water change, wait a week, then do another 50% water change.

Try to bring the 'new' water up to the same temperature as you have in the tank or at least to room temperature as well as adding Prime before adding it to the tank. This will minimize any shock to your beneficial bacteria, your plants as well as any fish that you may have already begun to add.

The 2 large water changes will help remove most if not all of the fertilizer without compromising your tank.


When I first setup my plant tank the first thing I did was add API Stress Coat and API Stress Zyme, Stress Coat is a water conditioner with aloe vera and Stress Zyme is beneficial bacteria. If you can get your hands on those or something close to it you'll want to double the dose of them for whatever size tank you have. It usually only takes 3 days or 5 at the most for it to be cycled. I personally don't like SeaChem and had A LOT of customers come to the fish store I worked at complaining about cycling taking too long or other issues happening when using it. Dechlorinator and Water Conditioners are basically the same thing just the difference between Prime and Stress Coat is that while they both remove chlorine and chloramines, Stress coat has aloe vera to protect the fish's slime coat and Prime doesn't have any extra stuff to help fish/plants.

Anyway when I had my 75g plant tank I just added the 2 I said and 5 days later I added some fish. I also used Floramax as the substrate mixed in with some bigger pebbles to hold the roots better.

  • 1
    this do not answer the question,it is about how to cycle a tank and you are not giving good advice on how to do this. Jan 31, 2018 at 8:16
  • @trondhansen I answered the question by stating to use liquid beneficial bacteria called Stress Zyme since the person asking was wanting to know how to do it without fish. Beneficial bacteria will start the nitrogen cycle the same as a fish would just without the fish itself. Jan 31, 2018 at 22:23

After many years and many tanks, I have stayed with my original plan: Put water in tank, do NOT use additives. After a couple days put in fish. This works for salt aquariums also. I occasionally use a trace of garden fertilizer, err on the side of less.

  • 3
    You shouldn't put fish in the tank without measuring the first and second nitrite peak, regardless of whether this worked for you once or repeatedly. Oct 6, 2017 at 1:08

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