high ammonia / low p.h

Question
QUESTION: I have had approx. 6 months of problems with ammonia in my tank and have been trying to work together with my local shop to fix the problem. It ended up that before xmas they took all my fish, we bought a new filter replaced gravel and started again.
In the beginning (about 3 weeks we couldnt get rid of the ammmonia) but after some consideration we decided it was because the ph was too low 6.2. we stared adding bi carb soda and amazingly when I raised the ph the ammonia disappeared. Then when the tank was perfect (only adding leaf zone for the plants) we started gradually adding a couple of fish at a time over a 3 week period. Everthing is still healthy and happy until.... 3 days ago we did a partial water change 33% added leaf zone, ammo lock and stress zyme. Now today one fish is dead the rest look crook, ammonia is at 2.5    nitrite 0.1   and ph 6.2
Could this combination of chemicals be toxic or could one be faulty (more likely the stress zyme) as its to the end of the bottle and for the last 6 months of troubles the ammo lock is a new bottle. Please note that all chemicals are still within their use by date.
As a matter of no choice i have added ammolock to lock up the ammonia today and put a little bicarb soda in to raise the ph. (also checked my tap water and it had no ammonia and a ph of 7.2

ANSWER: Hi Jackie,
This is a bit out of my league, but I suggest you call up your local water supply and find out what's in your tap water.
It's possible they add ammonia or Chloramines and regular test strips are not finding it.
I don't know what effect the soda will have on the fish, but it seems to me that the problem is most likely your tap water. You might also try using bottled spring water and adding aquarium salt and see if that helps.

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QUESTION: I have spoken today with my local water supplier and they assure me its not the tap water.
After my last message my pet store checked my water and said I needed to add a KH product as my readings were zero. Upon using this my levels were improving and after a week the water clarity also improved. I thought allmy problems were solved but to be sure a week later I did a partial water change only 25% and after 2 hours checked the Kh and all okay. I also added Amo Lock . Then about 6 hours later I started noticing salt like grains starting to form. Ever since now 5 days later I cannot get the Kh to stabalise (add 3 capfuls each day) Ph is trying to go acid now 6.4  Ammonia is critical 4.00   Nitrite is up and the tank is covered completely with this salt like particals covering everything and even forming string like patterns. I add Ammo Lock every 2 days because 1 fish is living in the tank (still appears happy). P.S I didnt touch the filter in this water change.
Any idears my pet shop is out of idears

Answer
Hello Jackie,
Okay, first - stop adding ammolock. It honestly does you no good. You need to instead work on getting your beneficial bacteria to grow. This is your biological filter and will take care of your ammonia for you.
Do more water changes - 30% each week, and continue to add ONLY the KH and water Conditioner. Any time your nitrates/nitrites go up, do a water change. Add some bacteria supplement like Stress Coat bacteria boost and keep the temp very warm.
Hopefully that will do the trick.