Goldfish, Carassius auratus auratus
Unfortunately to many people still don't know how to mature an aquarium. This leads to unintentional cruelty on their part and it is mainly due to lack of research and being all to ready to listen to old fashioned advice from some shop owners.
Fishless cycling has been around for decades, it is fast (when done properly) and easy to perform. No fish are put at risk and it is extremely cheap. Why consider any other method?
Almost all shops still recommend adding a few hardy fish to a new tank in order to mature it. So this is what most novices do. The result of this is that the new fish are subjected to high levels of potentially lethal toxins in the form of ammonia and nitrite. Anyone who works in the trade knows the consequences of this but they still persist in giving this advice.
If I were being cynical I might think that they had a motive with this advice because not all the fish used will live and so will need replacing. There is every chance the fish will contract white spot and so there is another sale with some remedy. Occasionally a novice will have done some research and will question this advice only to be told they are wrong and that the best way to cycle a tank is to use fish.
Initially the water in the aquarium will be absolutely fine, with no ammonia, no nitrite, and little or no nitrate. Soon after adding the fish this will change because fish excrete ammonia from their gills all the time. Because there is nothing to remove the ammonia in a new tank it will simply build up. Ammonia is extremely toxic to fish and even extremely low levels can prove fatal. If it isn't fatal it will certainly make the fish ill and uncomfortable.
After a week or so the ammonia will begin to oxidise in to nitrite. Nitrite is even more toxic at very low levels and it's effects can include asphyxiation, damaged blood, ulcers and death. The nitrite stage of the cycle can last for weeks when fish are in the aquarium and those new fish will be subjected to living like this for all of that time. I ask again why would anyone recommend this when they are aware of these facts?
If the fish survive long enough they will be very stressed and weakened by the experience and their immune system is compromised.. This leaves them open to infection and most commonly the infection which appears most is white spot. It isn't normally very serious and mostly it is easily cured but it will make the fish very uncomfortable because it makes them itch . Fish in such a poor state do not respond as quickly to the treatment as would more robust fish and so they will have this extra discomfort for longer.
There really is no excuse for subjecting fish to this treatment.
Bacteria in a bottle. These products have been around almost as long as the hobby itself. Very few actually do anything and at best they may help a little. The reason is simple, nitrifying bacteria cannot form spores and exist in a bottle. They need an oxygen rich environment with both ammonia and nitrite which is basically their food. The manufacturers of these products use heterotrophic bacteria instead of the true nitrifying bacteria. heterotrophic bacteria can utilise ammonia and nitrite but only at a fraction of the efficiency of true nitrifyers. It can take up to one million heterotrophic bacteria to do what just a single true nitrifyer can do, this isn't a problem when the product comes in a bottle because billions can be added at once and give the impression that the tank actually is cycling but heterotrophic bacteria prefer organic waste to ammonia and nitrite and so the tank really isn't cycled with these products.
This method was 'invented' specially for the internet even though there had been a commercial product on sale for many years before this which used an almost identical method!!!. It has been altered by people using intuition rather than knowledge and it is quite problematic in its resent form.
Commercial product: There is only one, Waterlife's BioMature. This isn't an instant cycle or a bacteria in a bottle product but it is an ammonia product and contains everything that the bacteria need to colonise an aquarium in the right numbers to be effective. It comes with full, simple instructions and it works. Then when the tank is properly mature the fish can be added safely. You only have to do this once so do it right and get off to a good start.
With all this in mind it does to us seem very difficult to justify using the old fashioned and cruel methods which sadly are all to often recommended.