Any of the "turd" colored cucumbers are not known for their toxicity. These are sand dwelling cucumbers, and not the colorful filterfeeding variety.
You don't want them to get chopped up in a powerhead tho, you're still dealing with toxic cuke guts that way....
BTW, the tigertail can get to 24" long....not for a small tank. Mine usually splits at 18". It also poops all the sand from the front of tank out as clean poop in the back of the tank....
