It’s not kalk… I’d guess 80% of sps keepers use kalk and it’s not a issue.. something was outta whack in my tank and I’m not sure what it was, as the norm cal,alk,mag,n03 and p04 were all in good ranges.. maybe a trace element was off I’m not sure? but when I started upping my dose of all for reef my tank fixed its self and I still use kalk in my top off. Once my acros started taking off and growing again the problem fixed its self thank gawd! lol… I don’t believe it’s lighting either or a bacterial Infection etc.. something in the biome/ or traces wasn’t correct and that’s my belief thus far and dealing with this. Happy to report it’s long gone thou! lol. Also happy to report zero losses! Just ugly and stunted growth on my part.