soft corals, calcium, ph

First of all, how much calcium do corals like xenia, mushroom, and zoanthids require in ppm? Does 400-500 sound ok? What happens when they are too high?

Also, I have been trying to bring my ph down for quite some time. My tank has been cycling for about 2 months now. The PH fluctuates between 7.7 and 8.0. mostly it stays at 7.7. How do i get it to the magic number of 8.3?

I have been breaking the water surface and just did about a 1/4 water change last week. If I have been using ro water do i still need to check alkinity?

One interesting thing i found is that the ro water is more acidic than then the water in my tank, my lfs said that was normal.. learn something everyday i guess.

 

The ro water when deionized is supposed to have a ph of around 7 which is significantly lower than a ph of 8.0 to 8.3
400-500 ppm calcium is a good range for the reef aquarium.
Alkalinity needs to be checked to see what it is, too high or too low will affect calcium levels. Chemistry and the Aquarium
It is my understanding that the salt mix you use determines your ph and how stable it is. If you go several months between water changes you may need to use a Ph buffer or maybe your test kit is not accurate.... 7.7 seems kind of low.

Jim