Optimal temp for axolotls is 16-18c, optimal temp for acf is 20-25c. Mixing species carries no benefits to either but does entail certain risks. Acf have claws on their hind legs, they have been recorded cutting fish badly with them, a soft bodied axolotl could potentially be seriously hurt by one. Axolotls will often remove limbs from tank mates, axolotls regenerate, acf do not, the loss of a front limb would potentially effect the feeding of a frog as they shovel food into their mouths, the loss of a back limb would effect swimming. Why risk either of these scenarios plus keep both species in suboptimal conditions ? As I said in my first post, some people keep these species together with no probs, it is how ever a risk I don't choose to take and I have plenty of experience with both species.