I have had my tank set yup for almost 2 months. i did a water change earlier my third one maybe. It appears my ammonia spiked.
It apears your doing must everything right you just ran into some bad luck.
After i read through this I would say you may have gotten some glass cleaner in the tank. That would be your ammonia spike!
Just a few thoughts I have on this topic.
I have seen the blue damsels turn white or gray do to 2 things, fear or aggresion from another fish, and rabid water temp change. I do not think from what you have discriped it was ick or velvet. ( yes ick does look the same as fresh water fish). If you should encounter ick a skunk cleaner shrimp will usally clean that up. An ultra vilot light would help too.
I have always used Instant ocean with no proplem. and your method of mixing would appear to be fine.
Add the carbon to your filtering system.
As for your glass lid thats ok, as long as it has a way of breathing (letting a good flow of air to get thru) you dont want it air tight.
After all the water changes it sounds like you have done. ( not actully knowing how much you have changed out) you may have lost the cycle.
Blue damels are one of the best fish to start up a tank with (IMO).
although for some reason I have never had any luck with clown fish. (I'll inquire on that later).
Stop, take a deep breath, check your system over again, and start over. I think you just made a error with the glass cleaner.
Cheer up, soon you'll be sneaking peeks in the middle of the night with a flash light, to see all the cool stuff that goes on in a salt water tank.
DILLYBOBS
