Post
by Hermias_mom » Sun May 14, 2017 9:48 pm
The main concern that jumped out at me from the posted picture was that the mesh is buried in the sub. If saltwater is used to moisten the sub, then zinc chloride is being formed where the metal mesh and saltwater meet. I'm a metallurgist, not a biologist, and I'm just learning about the biology of crabs, but from what I've read so far, zinc chloride evolution in the substrate can't be good. Here's an excerpt from the Wikipedia article on "galvanic corrosion ":
"Although galvanizing will inhibit attack of the underlying steel, rusting will be inevitable after some decades of exposure to weather, especially if exposed to acidic conditions. For example, corrugated iron sheet roofing will start to degrade within a few years despite the protective action of the zinc coating. Marine and salty environments also lower the lifetime of galvanized iron because the high electrical conductivity of sea water increases the rate of corrosion, primarily through converting the solid zinc to soluble zinc chloride which simply washes away. Galvanized car frames exemplify this; they corrode much faster in cold environments due to road salt, though they will last longer than unprotected steel."
As far as lids go, most reptile lids I've seen tend to have a powder coat (spray-on epoxy) black finish on them. If they are galvanized steel, but are not in direct contact with saltwater, but are rather in a moist environment, they shouldn't corrode as quickly, and the corrosion products may be different, but will still contain zinc. If the mesh is in a damp environment there's probably going to be some type of corrosion, but probably a lot less quickly. Basically, galvanized steel is manufactured by coating steel in zinc metal mostly using a wet process, where the steel is dipped in molten zinc. The zinc acts as a sacrificial anode by reacting with moisture instead of letting the steel react with the moisture, so the zinc corrodes before the steel does in order to protect the steel.
If your crabs are not directly crawling across the lid, an d are not coming in direct contact with it, and no powdery corrosion products are falling off the lid, as long as you don't touch the mesh and then go touch your crabs, that minimizes the exposure. Personally I'd recommend using powder coated lids when possible or plastic lids when you can. You can do some research yourself if you like and see how comfortable you are with your current configuration, but anecdotally the zinc kinda gets on my hands, and I'd have to do more research to see how easy it is to completely remove it from my hands and such. I'm not sure yet how effective soap and water are for this. Maybe just fine, but I don't know.
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4PPs and tons of FUN in a 29 gallon!
Hermia(F), Helena(F), Branch(M), and Tiger (M)
RIP Athena
(not pictured--salt water pool, food dish, other two coconut huts) haven't got that far yet 
