Ammonia Hell, HELP!!!

Hi!

I had a 55 gallon tank set up at the beginning of this year... I got a
whole bunch of plants and some fish. Everything seemed to go smooth
with the usual algea that disappeared after a while when I started
adding CO2 and fertilizing with K and Micronutrients.

At the beginning of june I noticed that I had a high amount of nitrates
(20ppm) so I decided to change the water. The ammonia was about 1 at
that time. I changed about half of the water. The nitrate went down by
about a half but at the end of next day ammonia climbed to 2. So, in a
hurry, I did another water change... and guess what... nitrate down by
50%. to 5ppm...ammonia up to 4!!!! To keep the water ph from crashing I
added some bicarbonate as a buffer since my tap water KH s zero.
As the days passed some of my plants started rotting .... limphonila,
narrow and wide-leaf ludwigas, some of hygro. The only ones left now
are anubias, chain-sword, amazon and bacopa.
From what I read, ammonia is more toxic at higher ph levels so I tried
not to buffer the water much... but the ph crashes very easily. On the
other hand I also read that the bacteria that converts ammonia to
nitrites and nitrates is more active at neutral ph levels and less
active when the ph is low. So, do I make my fish suffer while the
bacteria processes the ammonia or keep ph low to protect my fish but
risk ammonia not being processed. My ph is through the roof right
now... like more that 4 or even 8.
I was using Amquel previously to condition my tap water but now I have
AmmoLock. Could AmmoLock be the problem?

Thank you for your help and comments!

Additional Note: I stopped adding CO2 because after the ammonia hell
appeared the fish seem to struggle breathing when CO2 is added for the
plants.

Here's some entries from my tank log in reverse date order:

6/23/2006
8pm
KH:1
PH:6.5
CO2:36
PHOSPHATE:0.5
AMMONIA: high off the chart

6/22/2006
8:30am
KH: 2
PH:6.6
CO2: 15
AMMONIA 8?

6/20/2006
8:40am
KH:2
PH:6.6.
AMMONIA 8?
Added 3 capfuls of ammolock

6/11/2006
7:15pm
KH:0
PH: 6 ?
CO2:
AMMONIA: 1
NITRATE:
PHOSPHATE:
Added small teaspoon of Arm&Hammer Bicarbonate

6/10/2006
7:30am
KH: 3
PH: 6.6
CO2: 22
AMMONIA: ???

6/9/2006
6:15pm
KH: 2
PH: 6.6
CO2: 15
AMMONIA: 4 !!!!
PHOSPHATE: 0
NITRATE: 5 (7.5?)
Found one dead bloodfin tetra fish floating on surface
Changed about 40% water. Added K and TMG.

6/8/2006
6:30pm
KH: 2
PH: 6.4
CO2: 23
AMMONIA: 2
PHOSPHATE: 0.5
NITRATE: 10
Changed about 45% of water and Added K and TMG

7:30am
KH: 3
PH: 6.4 (6.5?)
CO2: 35 (28?)
AMMONIA: 1
PHOSPHATE: 0
NITRATE: 10
Added K and TMG

6/7/2006
6:25pm
KH: 3
PH: 6.6
CO2: 22
AMMONIA: 1 (0.85?)
PHOSPHATE: 0 (0.1?)
NITRATE: 20
Changed about 40% of water