How long have you used the Oceanic and what did you use before?
I would highly suggest testing a freshly made batch of your
SW after mixing and aerating for a good day. Please post
alk,
Ca, pH and
Mg as all will be needed to make an informed response. If you do not have one of these types, get your
LFS to do it for you. There are also several places online these kits can be aquired at relatively small exspense. Keep in mind each one will last close to a year if not longer.
It is a necessary exspense, especially if keeping invertebrates.
Oceanic has been linked to several algae blooms, more commonly
cyano and diatoms so there is a good chance it is your root cause. You also made mention awhile back that you use only flake foods for feeding. While there's nothing truely wrong with it's use, it can be an overwhelming source of organic
PO4 which will fuel
cyano unending. Many types of freeze dried and flake foods are augmented with a vitamin C substitute (
L-Ascorbyl-2-polyphosphate) that is loaded with organic
PO4 as is store bought fresh and frozen seafoods (
tri-polyphosphate). Although you haven't mentioned the size or type of the "sea shell" you aquired, it is possible for it to contribute to the problem albeit very small. As it dissolves, it will release any elements it deposited in it's growth, including
PO4.
If after a large 25% water change there has been no drop in your
Ca levels, this tells me there is one of three problems. The salt is designed to have that level of
Ca, the
alk is extremely low and/or the
Mg levels are too low allowing
Ca to climb independantly. None of which can be solved without knowing the results of the above tests.
As far as your question regarding the anemone, high
Ca will not directly impact the anemones health but there is no way of knowing how it will impact the ecosystem thereby indirectly affecting the anemone as well as the rest of your animals. You need to get the chemistry issue solved
before you consider any new animal additions.
Cheers
Steve