Originally Posted by whiskandbowl
Eeep...horror stories? Must have missed them when I was reading about cycling. Care to elaborate? I don't want to hurt my fishes.
Nothing dangerous. You can breath...LoL But you rarely hear about this stuff in a cycling how-to article.
Rotting fishfood or shrimp/fish can get Saprolegnia mold. It's not dangerous but it's not wholesome and its not easy to clean out once established. Some people think it causes Columnaris because it has a similar appearance. This is unsupported and not true. But it does get into your filter and onto your plants and decor.
Then there's the smell. Because the dose cannot be controlled, often the tank gets overdosed---the lag from decomposition makes this easy to do. You want the tank open so that bacteria can get in, but sometimes the smell makes that impracticable.
Sometimes the overdosing will stall the cycle. The too-high ammonia can kill the bacteria.
The cloudy bacterial bloom which sometimes accompanies a cycle, while harmless, is unsightly and can be worrisome if it persists.
All things being equal, if you want to perform a fishless cycle, I consider it worth the effort to get "pure" ammonia that does NOT foam-up when shaken.