Info on C02 Injection Needed

I have setup a DIY-Yeast C02 Injection system in a
1 gallon bucket to test things out.  The water initially
had a ph of 7.5, a KH of 3, and a GH of 6.  The C02 injection
has actively been injecting CO2 through an airstone since
last Saturday.  As of Wednesday evening, the ph had dropped
to 4 (I used 2 separate test kits to test it).  The KH and 
GH have remained unchanged.  By the way, I was using a 1 gallon
bucket as a test case to see how long the C02 would last and
what changes in water chemisty I would notice.

My question is, since I will be using this on a 55 gallon tank, 
will the ph drop as drastically since I am dealing with a much 
larger volume of water.  By the way, my ph, gh, and kh of the 
tank are the same as those mentioned initially and have remained
stable for several years now.

My 55 gallon tank has been setup for many years now.  The tank
includes 3 48" bulbs (triton, coralife, and original), an
aquaclear 300, and an undergravel filter with 2 penguin powerheads.
I have added over the last 2 months some 14 varieties of plants 
which include anubias nana, frogbit, pearlweed, banana plant, sunset
hygro, java fern, java moss, moneywort, watersprite, Broad, narrow, and
needle leaf ludwigia, gymnocorius, and amazon sword.  A majority are
doing quite well.  I do fertilize with only ferovit with my water 
changes (approx 1/3 of water changed ever 1.5 -2 weeks).  The tank is 
also well stocked with fish:

         3 medium angels
         4 ottos
         1 pl*co
         7 neons
         2 rams
         2 checkerboard barbs
         2 head and tail lights
         3 small clown loaches
         2 small pencilfish
         2 flame gouramis
         1 upsidedown cat
         3 corys
         a couple more small fish that I might be forgetting.

I'm concerned that I will kill my fish if I add the C02 injection
to the tank.  

Thanks in advance for any advice that you may be able to offer.
Marty Durkin