whats all this talk about crushed oyster shell calcium and calcium carbonate, saying the oyster shells can't be broken down. I use the rep-cal phosphorous-free calcium with d3 mixed with repcal herptivite w/beta carotene multivitamins, which contains "100% natural phosphorus -free oyster shell calcium carbonate." So is that all wrong just because its crushed oyster shells? I was reading this off Varnyards site.