Hello Gigi, my experience supports what Chinadog says.
There's a huge heap of scientific research done on tannins and amphibians most of which will tell you the data suggests a harmful effect of tannins on amphibians. However, although I'll take note of this information, I'll not get driven into a state of panic.
Firstly, this research has been examining tannins in an aqueous environment using concentrations of tannins frequently above those found in natural pools. Sure there are forest pools and forest (particularly oak) run offs which visually resemble black tea, but are you likely to keep amphibians in this in captivity? Near my home, the palmate newts seems to prefer small, peaty pools and some aquarists actually add tannins to their tropical fish tanks as a water conditioner. I've done so, using extracts and bog wood, with my south American animals. The main reason for doing so is to reduce the pH. I'm thinking black water conditions here. In these aqueous environments, the amphibians' skin would be bathed in the tannin solution and this could be the main issue relating to harm.
Secondly, the concentration of tannins in leaf litter might be high if they were put into solution. But they're not, and so their actual contact with the amphibians, although will occur, are unlikely to be at a level to cause harmful effect. It has been suggested that leaf litter could be rinsed until the water runs clear, but this seems like a knee jerk reaction. I keep a whole range of Salamandra subspecies. A quick check up of their natural localities and habitats will tell you that they are found in oak and beech forests hidden amongst fallen logs and often buried in leaf litter.
In my early days of Salamandra keeping, I panicked every time I read an article where someone recommended a system which contrasted or disagreed with mine. I read, trialed a new approach, adapted it etc etc all the time noting how well my animals were until I had a system which gave me confident. My animals are in top health and condition and breed each season. If they didn't, I'd have to rethink.
I tried several substrates ranging from damp tissues (I know this sounds very clinical but has many advantages but it's not for me), coconut fibre, additive free peat (this would be my scone choice) and leaf mold. For me, the number one substrate which I'd use every time is leaf mold from beech, oak, sweet chestnut forests etc. I'd avoid any from coniferous forests. The needles contain high levels of phenols. Tannin is a type of polyphenol. Seems like we are headed back to the beginning again n this one.
Gigi, you're doing the right thing by asking these great questions and in a place like this you'll get valuable real life experience. Check the Internet though, but don't believe everything you read.
