Aloe vera may be natural in the sense that it grows and isn't synthesised in a chemical plant, but is it naturally occurring in rivers and lakes? If not, it is not natural for fish to become coated with it.
Using aloe vera adds organic waste to the tank. API say that they don't recommend the aloe vera containing Stress Coat in tanks with protein skimmers (marine tanks), which are designed to remove organic waste. Presumably the protein skimmers work overtime and get clogged up or whatever happens to them..
Some one on another forum is fond of saying that everything we add to a tank ends up inside the fish. For this reason he advocates adding a little as possible to a tank.
