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Fishless Cycling Data

Below is an account of an actual fishless cycle. This data has been contributed by William Wallace from the US, one of our forum members, who was particularly thorough in tracking the cycle in his tank!

Well, I tried a fishless cycle for my 75 gal tank and it looks like I'll be able to add fish in 2-3 days. Figured I would post this here in case anyone else was considering trying this method.
Date (US format)AmmoniaNitriteNitratepH
(re-read the article and added NH3 to cause a spike)
(added driftwood that was from a tank at a LFS)
(no new NH3 was added until the ppm started to drop)
(after ppm started to drop, half the dose needed to cause the spike was added daily)
(CO2 added to help with pH, added tons of plants)
(a small water change was done when NO3 was >20)
(the daily dose of NH3 was added after the water change, if one was done)
(I expect a continued drop in NO2 over the next few days)
(When I go 24 hours with both NO2 and NH3 zero I will do a 25-50% water change and add fish)
(Looks like a complete cycle in 12-13 days. Not bad and no fish hurt or lost in the process)
(I see a trip to the LFS in my future)
Added some fish: current size in ( )
1 angel pim (4") was in a holding tank
1 spotted talking catfish (4") was in a holding tank
8 ottos (1") (to cure the green alage problem that developed)
2 [m/f] Pearl Gourami (2")
3 Clown Loaches (2.5")

If all goes well I'll add some mid/upper dwellers this weekend, but I'll only add 5 fish/week until I get all the ones I want.

(All the fish look healthy)
Sad to report one death, a healthy appearing otocinclus found drifting in the currents. No sign of trauma, ick or other disease. In fact he had a round full normal looking belly, as any happy otto should. Of course Ottos are known for these mysterious deaths...

The otto is survived by:

1 Spotted Talking Catfish
1 Angel Pim Catfish
3 Clown Loaches
1 Flying Fox
2 Pearl Gourami
1 Neon Dwarf Gourami
1 Cinnamon Dwarf Gourami (deep dark red)
7 Otos (originally)
5 Blood/Serpae Tetras

All appear well and active... except the spotted talking Catfish who goes missing for days then shows up happy and healthy caught out when the lights flip on.

One Note: The NO3 is a funny thing it has dropped from 20 to zero without water changes. I credit this to the many plants some of which are fast growers.

10/21/01 Just some follow up notes.

1) fishless cycling builds up such a nice populaton of bacteria that I have never noticed any NH3 or NO2 after adding fish ... even when I added six 2" diamond tertas.

2) only fish lost were 3 of the 8 otocinclus ... but that is on par for that type of fish being added to any tank.

3) current and final stock:

1 Spotted Talking Catfish, 1 Angel Pim Catfish, 3 Clown Loaches, 1 Flying Fox, 2 Pearl Gouramies, 1 Neon Dwarf Gourami (sold as "Rainbow Gourami"), 1 Cinnamon Dwarf Gourami (deep dark red with white tail), 5 Otocinclus (lost 3 from original 8 added), 5 Blood/Serpae Tetras, 6 Diamond Tetras (bought 5 but found I had 6 when I got home), 2 YoYo loaces (wanted 3 but only 2 left at the store), Tons of Plants!

So set up tank on 10/09/01 and now a mere 40 days later I have a nice mature fully stocked tank.

Edited by Sean, for typos/clarity only


  • Plants may have unpredictable effects on a fishless cycle, because they will compete with bacteria for the ammonia. They are an excellent way to help introduce the necessary bacteria, but it should be noted that adding a lot of plants may alter the profile of the cycle, and make it more difficult to establish a large population of nitrifying bacteria, although the plants themselves will compensate for this to some extent.
  • Certain rocks (especially very porous or soft/crumbly rocks like tufa), may absorb ammonia and other nitrogenous wastes when levels are high, leaching them back into the aquarium at a later date when levels are lower. It may therefore be better to add such decor at the end of the cycle.


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