I too have been advised against using products like ammo lock - it doesn't allow the tank to ever finish cycling.
Your water change should not have caused the cycle to crash - good bacteria lives on the filter media, decorations, plants & substrate (not in the water itself).
It's important to do frequent water changes to keep the toxic levels down whilst the bacteria establishes itself as mentioned above. Never wash or scrub your decorations and stuff, if they are really dirty, just swish them in the dirty tank water from your water change.
Good luck :happy:
Ps - as peatea says, 20% daily water changes should be enough, personally I'd not do any more than 40% at any given time. Read up on cycling, there are plenty of threads on here where members have had similar problems.