tank crashing!!! from too high ca???

[matt_54351]

I overdosed limewater and shot the ca through the roof. i maintained proper ph (8.1 at am, 8.3 just before lights off) through the whole dosing, and ever since. i used vinegar to drop the ph of the limewater down to a reasonable level so the ph never spiked high. i checked it 10 times as i was dosing the tank and immedately after, and the ph stayed stable. the snowstorm came after about 12-15 hrs (in the middle of the night) and everything seemed to be fine for about 24. ph stable as well as all other levels staying normal. i was just going to wait it out for the water to clear up, but i woke up this morning (48 hrs after dosing) and 3 fish are dead, all snails are dead, frogspawn and softies look horrible, anemones look horrible, and after a full blown water test i get this:

ammonia, nitrite: 0
nitrate:15-20
phosphate: .3-.4
ca: 500
alk:10 meq/L

any guidance would be helpful, and yes i am doing a 30% water change right now, trying to force myself not to do more. posting while i wait for the salt to fully dissolve.