My two CDTs live outdoors 12 hours a day and eat grasses, weeds, greens, cacti and veggies. I bought one of those ZooMed cactus/calcium blocks 6 weeks ago and they've shown no interest in it. But I've noticed them nibbling at rocks and dirt in their enclosure, and I wonder if I need to add a calcium supplement. I see Rep-Cal has one that comes without D3 and phosphorus. Is that what I should get?