Kiwi likes to destroy cuttlebones for the sake of destroying them. He doesn't actually ingest much, just tears them up (flings huge chunks of it everywhere). I agree with weco that if the bird is actually eating cuttlebone in huge quantities, there is likely a deficiency that should be addressed. If not, he may just enjoy ripping them up. The best thing to do is to keep your eye on him and see what exactly he is doing with the cuttlebone to make it disappear that fast (senselessly destroying or actually consuming huge quantities).
Also, I'm not entirely sure where conures are native to (I think south America right?), but there is "Manu clay" blocks sold for parrots as well. I believe they are only intended for the south American birds that eat it naturally, but I notice Kiwi doesn't destroy the clay blocks, and one of those will last for months in his cage (he just nibbles on it here and there). There are also commercially made mineral blocks for other species of parrots that are a little harder than cuttlebone, thus more difficult to for them to destroy.