Stability

So, I'm not new, but not a pro by any means. What is meant by having a stable tank, we dose daily, and it stays close to the same but not perfect that would be stable right? Right now these are my parameters:
alkalinity: 11.2
nitrates: 1.25
ammonia: 0.2-0.4
calcium: 500
magnesium: 1600
So I am just curious what do you mean by unstable, the parameters vary (we test twice a week), but we do what we can to keep them very close by dosing accordingly from the test before. My GSP seem to have shortened their green tentacles, but everything else seems to be doing okay, except my green button polyps. I have USACurrent marine 48 inch LED bar on 55% blues and 55% whites. Button polyps are on the sand, and haven't moved them, but they have been two lonely heads since the hurricane in New Orleans in 2012. They haven't died, but they barely open if at all. Lights are on for about 12 hours a day, and slowly come on and fade out like sunset and sunrise. I have two powerheads but seemed like it was too much for the hammers, and I was right, so no neither are on, but the pump cycles a lot of water and has lots of flow already. Any insight would be great
 
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