its been a while i been using K2R reactor. my calcium is 550. what will happen if calcium is this high? is it will kill my coral or fish? the tank is 55 gallon .
It will precipitate out and you'll see it. Turn down the reactor if you can. 550, although too high, isn't too bad. Test more with other test kits to be sure that it's really 550.
Make sure your other params are acceptable.
Check your Mg level.
It is my understanding that there is a trade off at some level between really high calcium levels and high alkalinity. I think you sustain a higher calcium level with slightly lower alkalinity. you might see what is going on with you alkalinity
my calcium is 550. what will happen if calcium is this high? is it will kill my coral or fish?
A calcium level of 550 ppm is a bit high, but probably not a problem on a tank with a reactor. What to do about it will depend on the alkalinity level. High calcium can often depress the alkalinity.
If it is on the OK to low side, I'd add an alkalinity supplement not balanced with a calcium supplement to allow the calcium to drift down. Sodium bicarbonate (baking soda) or sodium carbonate (washing soda) would be fine.
If the alkalinity is on the high side, then you should just dial back the reactor to nod add as much calcium and alkalinity.
This article describes the various ways that calcium and alkalinity interrelate: