RO and pH issues.

I use this:
http://www.kentmarine.com/sal****er/opm.html

CW
"George" wrote in message
news:2uo8e.21314$xL4.5103@attbi_s72...
I have a 35 gpd Ro unit (with carbon and sediment filters, no DI filter).
I've been reading up on RO this evening and found several references that
say that RO water can be more acidic than tap water (lower pH) because RO
membranes do not reject CO2. This concerned me since I've been having
water quality problems for some time and thought that it might be a problem
with my sea water not having enough calcium. I bought a Nutrafin pH test
kit and a Nutrafin Calcium test kit. I got some interesting results. For
the tap water, I got a pH of 7.5 with 60 mg/L of calcium. At present, the
water in my marine tank has a pH of 7.5 (yes, I know it is too low) with
calcium at 280 mg/L. The RO water has a pH of 5.0! Calcium was
essentially 0. I don't know if it is normal for the pH to be so low in RO
water, but I suspect that adding this water unbuffered to my aquarium is
the root cause of my problems (thankfully, I have quite a lot of sea sand
in the tank, so it does prevent a pH crash below 7.5.). I understand that
RO units do not always result in a substantial drop in pH since it depends
on the amount of dissolved CO2 gas that is present in the feed water.
Apparently, my tap water has a high CO2 content.

This is a good argument for strict testing of make up water, especially
since, in my case, I never tested the pH of the RO water, assuming that it
was neutral (which it is obviously not). I plan to start adding sodium
bicarbonate and calcium chloride to the RO make up water in the future,
and aerating the water for 24 hours prior to adding it to the tank. My
question is does anyone know of a computer program that I can use to make
calculations of how much of each to add? I can do it manually, adding a
little at a time, but it would be nice to be able to calculate it in
advance in order to approximate what is needed so that it doesn't take so
long to do or use up the expensive test kits. Another question. Since I
am going to add calcium chloride (turbo-calcium) and sodium bicarbonate,
should I also be worried about adding magnesium to the make up water?