I see the connection of BDBS and corydoras whiskers and bacterial lesions on stomachs all the time.
I think one of the issues is the whole conversation is very much my anecdote vs. your anecdote. The fact that an expert has his own anecdotes is by no means any sort of definitive proof.
The whole "it's not natural" argument doesn't hold any water for me either. Nothing about keeping tropical fish in small glass boxes is natural. Fuller points out that many corydoras live on a substrate of mud and mulm, and while that works in nature it doesn't in our fish tanks.
In order to cut through the confirmation bias/Baader-Meinhof phenomenon that this topic is subject to, I did a search for "corydoras damage barbel" on google and indexed the forum results based on website, species, and substrate. A few notes on the methods:
- I did not include results where the author did not mention their substrate type, or where the author the athor was not specifically talking about observed damage to their corydoras' barbels
- In general, people are far more likely to use sand or gravel in their tanks than other substrates, therefore you would expect to see these show up more often
- I did not find any tanks with BDBS in the first 15 results, so I did another search isolated to ThePlantedTank since BDBS is often used for planted tanks.
- Sample size was very small seeing as I have a job I'm procrastinating doing right now. That said, unless somebody can come up with a better set of observations it's the best we currently have.
Full results are below.
The results from Aquariumadvice.com and Fishlore (n=8) were split equally between sand and gravel. Only one of the sand results specified a type of sand that MIGHT be similar to BDBS, Caribsea's Tahitian Moon Sand. Two specified "soft sand."
The results from Plantedtank.net (n=9) were 5 Eco Complete, 3 sand, and one gravel. None of the sands were BDBS. Maybe I have a skewed perception of the number of people who use BDBS on this forum but I would expect that if it was bad for cories, at least one tank with BDBS would have shown up. The big surprise was how often people who use Eco Complete reported damaged cory barbels, especially considering it doesn't seem like that many people use it as a substrate.
Overall results suggest that sand (any sand, not specifically BDBS) might be marginally worse than gravel, though this is most likely due to a larger amount of the population using sand for cories than using gravel. Eco-complete was the worst. BDBS and and clay-based aquasoils didn't even show up, implying that they might be good candidate substrates for keeping corydoras barbels healthy.