Salt can be used on ich and some other diseases. Fin repair solutions contain aloe extracts. In fact, most every one of the bottled products are simply purified and concentrated naturally occuring substances. (for a one line summary just go to the bottom)
The ammonia in a bottle is the exact same chemical as in fish wastes. The bacteria in cycle, bio spira, and bacter vital were cultured from the real world. Medicines, including antifungals and antibiotics, were derived from naturally occuring compounds. Most every compound we use in everyday life is a purified natural derivative, or a slightly modified version.
These products are around because they work, and work precisely. I think anyone would be hard pressed to diagnose problems in their water parameters without them.. We wouldn't know when the cycle is done, or what kind of water we are putting our fish into without them. A "fishy cycle" is natural, but causes undue stress to fish by exposing them to elevated levels of ammonia for prolonged periods of time. The fishless cycle uses the same product to achieve the same end goal, without stressing fish.
Plants, bacteria, and animals live in the nitroogen cycle, and that's what we are trying to mimmick in our aquaria. However, since we are limited in space (our aquaria, no matter how big are puddles compared to the natural habitats of fish) we use natures same mechanisms on a larger scale.
Nitrifying bacteria live at the bottom of any body of water. The substrate and a porous substrate allow the bacteria to live at larger concentrations than in the wild. They still do the same thing, just at a much larger scale.
In summary, virtually everything in the aquarium world is a natural mechanism on some level- either directly or a derivative of a natural mechanism. Companies have simply manufactured a purified and concentrated form of it.
