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Also, you had mentioned the ideal conditions regarding temperature and what not so I will just ask a straight up question since I don't know the answer...
Should you not ideally cycle your tank, fishless or otherwise, under the same conditions you intend to run it? if you grow the bacteria at a certain temperatu re and then change it, do the changes in condition not have an impact on the bacteria and trigger a restart to the cycle process? I know that back-in-the-day people had used gold fish but they were prone to disease at high temperatures and then swapping them out and putting in tropical fish re-triggered the process to start again. I thought temperature change played a role in that.
This is the kind of good question that observant people -have- asked since the 1980's when fishless cycling got started. We -do- have answers and observations about this. If you had no shared experience from others having tried and reported what happened to them then using final fish conditions would indeed be a sensible starting point, but luckily we have hundreds of cases (even from just the last few years here on TFF) from different forums and even some scientific papers that pertain.
The first thing to understand is that using fish conditions -will- work for fishless cycling (makes sense) but it is slow. Temperature, pH and ammonia concentration are among the most significant variables. The biofilters for both tropical and cold water turn out to harbor the same two species (Nitrosomonas spp. and Nitrospira spp.) It's been confirmed many times that seeding/cloning filters can work in either direction for these. When fish are not present however, we have the advantage of being able to use the laboratory growth curves for these autotrophs: The optimal growth speed peak is rather sharply centered on 84F/29C (28,29,30C) and looks like a rounded pyramid (roughly, temps around 20C and below cause very slow metabolism and temps around 40C and above cause the cell proteins to be inactive and can possibly cause membrane failure.)
The optimal pH curve has a larger flat plateau running from 8.0 to 8.4 and is important for different reasons in different phases of fishless cycling. During the first phase of fishless (prior to the nitrite spike, when you are trying to grow the first A-Bacs and get ammonia to drop for the first time) it's advantageous to not have pH below 7.0 because below that, the enzyme in Nitrosomonas that carries out the first part of ammonia oxidation is rendered inactive. (It's easy to see the problem here with low carbonate alkalinity, since once the A-Bacs ramp up (NH3 -> NH2- + H+) protons are grabbing all the carbonate ions!) Then, toward the end of the second phase when nitrites are sky high and during the 3rd phase when nitrates are replacing nitrites, we have the same excess proton problem but this time it's caused by the 7% nitric acid you get when nitrates are dissolved in water as the nitrogen complex moves back and forth between the nitrate ion state and the nitric acid state. This second one causes much stronger downward pH pressure.
OK, so now for the one most closely associated with your question, the ammonia concentration. The most interesting limit we find here is that concentrations at about 8ppm or higher will encourage a different species of A-Bac that can cause significant problems (it flourishes and occupies the media sites but then dies when there are drops in concentration and the dead material won't give up the media site) [Note: it helps to understand there are hundreds of species present in the fresh water and our autotrophs typically aren't more than 10% of what's there. There are lots and lots of heterotrophic species present.] But below 8ppm, our ammonia will correctly encourage the Nitrosomonas and this will be true anywhere from zero on up the point at 8 where it will be outcompeted. In hobbyist filters, the most optimal concentration at a given phase of fishless is based only on our crude observations and a precious few comments from the scientists. I feel an initial hit of 4 to 5ppm in the very beginning is somehow beneficial (perhaps there are other organics that may tie up some of the NH3/NH4+ or larger amounts may somehow ensure better final delivery to the sites on the biomedia where we want the molecules to be.) Then, once the second and third phases are reached, the whole picture changes and it's all about limiting the push of nitrogen because the process is going to drive NO2- and NO3- so high, so we drop down to 2ppm or so to reduce the number of water change disturbances we might have to do. Then in very final run, we always want to ease the dosing back up to 5ppm because we need to prepare the now much larger colonies for the big drop down when we remove the artificial ammonia source. The drop-down is extremely important and is one of the prime reasons why we have developed the "qualification week" add-on.
There are still other important factors but they are beyond the scope of this article: the DO (Dissolved Oxygen) level is quite important and it's true that the acceleration we seek with the 29C temp could be slightly negative by lowering DO, which is why surface movement (and added aeration in some cases) is very important. The list of trace things that kill our autotrophic bacteria is long and most of us can test for none of it: aerosols (N2O), Copper, Nickel, Zinc, Cadmium, Chromium, Methanol, Ethanol, n-butanol, Sodium Sulfide, Ethyl xanthate (mining industry), Disinfectant, surfactant, fabric softeners, shampoo, UV light, even H2N2 (rocket fuel!
)... these have all been found it home water supplies at times.
Another important argument that's been raised is that in fishless cycling we aren't pre-growing the heterotrophic colonies that will be a part of the finished freshwater ecosystem (the many species that will contribute by breaking down the fish waste and plant debris to add to the main ammonia coming from fish respiration.) This is a non-issue, I feel, because the heterotrophic bacteria are so very, very fast and ubiquitous. They double within 20-30 minutes, as opposed to the 2 days that autotrophs can take (hets can use organic carbon, whereas autos can only use CO2 for carbon, which is slower.) If you've ever seen a bacterial bloom form, then you know how fast the heterotrophs can appear and then disappear.
~~waterdrop~~
