Hmm I think that's a little small. I have mine in a 14 gal, I would say 10 minimum to give a couple of them enough room to have sufficient water and land. In a 3.5 gal you could have as little as 1 gal or less of water in there and I've read it's hard to maintain proper SG in that little of water. I keep mine with at least 4 gals of water. I've seen lots of set ups that had very little water and while I do think they need quite a bit of land, I think more water than they are often given would be appreciated. I would say mind spend 50/50 time in water and on land. I had one male get so big I can't imagine keeping him in a 3.5...often they seem tiny when you first get them but after a few molts they can really get pretty big.