Technically you could hold off on the reactor for now if you want. Those corals wont suck that much Ca out of 180G of water. Your regular water changes should look after it no problem and you can always "tweek" the levels as necessary with 2 part.

Here is some homework reading if you're interested is some better understanding of the relationship between CO2, Alkalinity and pH.

Low pH: Causes and Cures
http://reefkeeping.com/issues/2004-09/rhf/index.htm

just tested my alk its just over 6dkh

well that was easy
i put in 40ml of B into DT and 40ml of A into sump
now the ph is 8.16!! woot
i was going to do 40ml for next 4 days but maybe ill stop after the pH hits 8.25ish

If your PH is 8 you are OK I found that my fish did not like it when my PH went down to 7.8 or lower I do use kalk KH buffer with mag in it to get extra CA in the tank and to raise the PH to between 8.1 and 8.2. I do not use reef buffer as it has to many things in it from what I've heard. I don't trust a product that does not list he ingredients on the label.

Bill

Remember to raise or lower levels gradually (too big a sudden change is usually a bad thing in reefing). When messing with water chemistry, raising one element usually affects other elements, so don't go overboard with sudden changes.

Well I came home to about 8.07 PH and I dunno if its just me but the tank seemed more "active". I guess the fish were a bit unhappy with the low ph?
Also the aenonmes are now "thickening" up.

You are only seeing pH move as a side effect of what you are doing to Alk...and likely the particular timing of WHEN you read the pH.

It seems like you are adding A/B based on pH measurement, when you should be adding A/B ONLY based on what you are measuring for Ca/Alk.

When you have your Ca/Alk rock stable...THEN you can start thinking about ways to manipulate your pH. Until that point, you should not be concerned about what your pH appears to be.

yup thats what i did (sorta) i was trying to raise my DKH which I have done now i believe. But i did also dose the Ca but forgot to buy a test kit to test what it was! doh.

Try opening your windows if you don't already. Low pH in aquariums is often a problem when CO2 levels in a house get high. CO2 is acidic, and often some fresh air fixes the problem right up. I have this happen every winter, but it could be a problem for people with air conditioning who don't open up their house every now and then.