Hole eaten in my giantcup

[Titus07]

Anyone have any ideas what is going on here? My giant cup is dissolving and I cant seem to stop it.

[gflat65]

Hmmm. I have a gold crown sarcophyton that used to do that. It would turn white in spots and the spots would go deeper and deeper until a piece fell off, or it reached the edge. They don't do that any more (or haven't in a few years), but I'm not sure what I did to stop it. Check your Alk, Ca, and Mg and see where you are. How often do you do water changes? Do you run carbon?

[Titus07]

100g total water. 20g change a month. All chemical measurements look fine. 78degrees, 1250mg, 430ca, 11dkh, ph 8.2-.4.