I wouldnt worry too much about hermits, unless you have some exotic snail of some sort (with a really pretty shell
). Sounds like they will have their claws full anyways.
I wouldnt dose anything unless you are testing for it. I think that too high magnesium can cause the calcium to precipitate (or something else). (Been a few years since I had Chemistry for Majors).
Yeap, bulbs are $$$! (For us poor people anyways). Those actinics shouldnt contribute at all to the algae (or corals though). If your 13W fluorescent lamp is close to the chaeto and giving it good illumination, it probably is fine. I have one of those spiraled CFL bulbs pointing near my chaeto clump and the stuff is growing.
Yea, timers are so nice! Very helpful little devices!
You may want to cut down on lighting time until you can get those older bulbs replaced. (Assuming they are the true problem).
I dont remember if you use GFO
or not, but its something to try out. I have been running it in my filter and it seems to be helping. (Had a quick reduction in brown whispy algae).