The ammolock is better than the ammonia removing filters. The ammonia removing filters starve the filter bacteria, stopping the cycle from working. When they get saturated, they stop working. In turn this will lead to a killossal ammonia spike

Another case of poor advise from the LFS. They will sell you anything that gets you to go back there regularly, as that generates more revenue for the owner.

My experience with Tetra safestart is that it is a waste of money, as it does not work. By all means try it now you have it, but don't expect it to work any miricles for you
The large fish have to go. They will become an issue if they aren't the issue already, cleaning out the tank for you.

If you don't have a suitably large tank for them, it's LFS time again, they will have to re-sell them for you on your behalf. The quicker you get shot of them the better as far as the current situation goes. I know as keepers we get attached to our fish, and re-homing them is tough, but it is something you must do for their welfare
Ammolock converts ammonia to ammonium, which is about as toxic as nitrate i.e. not very

This is a "quick fix" solution to the issue of a cycle and does nothing for the following nitrite spike, but it can give the fish temperary relief from ammonia's effects. Salt is good also in a cycle, as it reduces nitrite toxidity. Once the cycle is done though, you should discontinue use, as many research papers have surgested that it has very bad in long-term use, as it increases osmosis pressure on the fishes internal and exturnal organs and control processes. Short-term during a cycle, salt good. Long-term health tonic, salt bad
With ammonia up, do another large (as close to 100% as possible) waterchange to check it. If you can, get some ammolock in this situation, as that ammonia spike needs to be controlled to keep the fish alive.
On a side note, are you shure the kit is fine? Could you take a sample to the LFS tomorrow to compair results? If so, make shure they use a liguid or tablet based kit, not strips, and most importantly
get them to write numbers down don't accept "it's fine" as your results, as what they call fine will be like ifinate ammonia, nitrite or nitrate levels if the rest of their advise is anything to go on
All the best
Rabbut