20 Gallon Tank Fishless cycling, multiple problems encountered!!

  • #1
Are you doing a fish in cycle, fishless cycle or was your tank cycled and you had a sudden ammonia or nitrite spike?: fishless cycle

What is the water volume of the tank?: 20 gallons
What type of water are you using in your tank? (tap, well, RO/DI, other): tap
When did you start cycling the tank?:
May 9, 2022
What type of filtration are you running on this tank? (sponge, HOB, canister, other):
If canister or HOB list all the media you are running in it. (manufactured cartridges, sponge, etc.):
manufactured carbon cartridges and bio-filter sponge
Do you have good water agitation/surface movement?:
Yes from the filter flow and a bubble stone
What is the water temperature?:

If fish in cycling - N/A
What is the entire stocking of this tank? (Please list all fish and inverts):
How often do you feed them and how much?:
Are they showing signs of distress? (fish hiding, staying at the top, looking pale, torn fins, etc):
Do you have live plants in the tank?:
If so are they healthy and actively growing?:

Products used while cycling
If this is a fishless cycle what ammonia source are you using? (fish food, Dr Tim’s ammonia, other): Dr. Tim's ammonia
If adding liquid ammonia how often do you dose ammonia in your tank and in what quantity? (1ppm, 2ppm etc.): Dosing weekly only after the ammonia and nitrites drop to 0ppm
If using fish food as your ammonia source how much are you adding and how often?:
Are you using a dechlorinater and if so, which one?:
Yes - Tetra AquaSafe
Are you using bottled bacteria and if so, which one?:
Yes - API Quick Start
Did you add seeded media from a previously cycled tank?:
What other products/chemicals are you using? (list them all):

Testing and cycling process
What was your knowledge of the nitrogen cycle before beginning to cycle your tank? (none, beginner, intermediate (please explain), advanced): Beginner; have had fish tanks in the past but never understood the nitrogen cycle. Researched the process and decided to go with fishless cycling to prepare a tank for an axolotl
What do you use to test the water? (API liquid, test strips, other): API freshwater master test kit
Did you test your tap water for ammonia, nitrites, nitrates and pH, if so post the results below?:
Yes, see parameters below.
Have you done any water changes and if so, when?:
Not in the beginning, which was a mistake and began growing white fuzz/algae around week 2 (problem #1), but now doing at least 25% w/c weekly.
How much water did you change?:
at least 25%, will change more if nitrates get too high
Did you vacuum the substrate?:
Did not until black bacteria began growing under the sand substrate around week 8, then vacuumed out all the sand and rinsed with fish tank water to remove black bacteria (problem #2)
Did you clean your filter, filter media, decorations and/or glass?:
Yes, around week 8 after discovering black bacteria
If using disposable cartridges have you replaced one recently?:
Did not change filter cartridge initially until week 8 (problem #3), last changed on 6/30/22

*Parameters - Very Important
What are your parameters? We need to know the exact numbers, not just “fine” or “safe”.
Tank water:
0ppm 24hrs after dosing ammonia
2-3ppm 24hrs after dosing ammonia
40ppm 24hrs after dosing ammonia

Tap water:

I set the tank up around 5/9/22 and dosed the ammonia up to 2ppm. After 2 weeks, white fuzz/algae began to grow on the fake plants and log, and I took them out and cleaned them, and did a 25% water change, which didn't seem to stall the nitrogen cycle at that point. Ammonia readings were 2ppm for 3 and a half weeks, then dropped to zero and nitrites spiked to 4-5ppm. The white fuzz/algae returned around the same time, but I did not clean the decor this time, and it disappeared on it's own. The nitrites stayed around 4-5ppm for another 3 weeks, then dropped to zero. Thinking my tank had cycled, I went to do the final test to see if the bacteria could process 2ppm of ammonia within 24 hours. I dosed up the tank to 2ppm ammonia on 6/25/22 and the ammonia dropped to zero within 24hrs, but the nitrites would only drop to 0.25 after 24hrs. Around the same time, the PH began dropping to 6.0-6.2, so I did a 50% water change on 6/26/22, and while moving around the fake plants, discovered black bacteria growing under the top layer of the sand substrate. We only have approximately 1.5in of sand layer in the bottom of the tank, and everything I read online said that the black bacteria should not grow in sand less than 2in deep, however, it was everywhere, and smelled horrible like sulphur/rotten eggs. Not sure of what to do at this point, I decided to vacuum out all of the sand into a pillow case, and wash it using syphoned fish tank water, to oxygenate the sand, and kill the bacteria (now I make sure to stir the sand at least twice a week, and have staved off any further growing black bacteria). After the black bacteria was found, the tank has not been able to process the nitrites to zero in less than 48hrs, so I'm thinking I killed off a ton of the good bacteria. I also probably waited way too long to change the carbon filter the first time (changed 6/30/22). I've been dosing ammonia weekly since the end of June, doing 25% water changes weekly, but not seeing progress in the nitrite processing time. Wondering if I'm just being impatient now, especially in light of all the problems I've encountered along the way?
  • #2
I will say just be patient right now and stop changing any filter media. A lot of your good bacteria was tossed with that filter.
  • #3
Do not change any filter material when cycling a tank. The carbon is not needed. Better to replace it with filter sponge.

As you said, you probably disrupted the cycling process somewhat when you cleaned the substrate. A less disruptive approach would be to vac the sand. If you use a Python type gravel vac it may suck up the sand (not good). If it you use it to siphon the water instead of hooking it up to the faucet it will have less suction and will only tumble and clean the sand. Stirring it as you are is good too if there is sulfur gas accumulating(hydrogen sulfide, I think).

Your tank is so close. Don't despair.
  • Thread Starter
  • #4
Thanks for the advice. I'm doing a water change today before leaving for a week's vacation tomorrow. I'm hopeful that when we get back the tank will be ready!
  • Thread Starter
  • #5
It's been a few weeks and I'm not sure if my tank is fully cycled, as I've seen some places say it must cycle 1ppm ammonia to nitrates in 24 hours and others say 2ppm in 24hrs. My tank can currently process 1ppm ammonia to nitrates in 24hrs, but it takes 48hrs to cycle 2ppm (ammonia goes to 0 after 24hrs, but the nitrites take longer). Am I cycled?

Similar Aquarium Threads



Top Bottom