Stop using the ammo lock, just use Prime.
Hmmm... If you just spiked to 8 ppm, you might well lose fish if you stop using the ammo-lock altogether at this point. Some ammonia is needed for the cycle to get going, to be sure, but it sounds like you'll have way too much, if you give up on the ammo-lock now, especially if your tap water coming in has 2 ppm.
Here's a thought: you could keep using the ammo lock in your main tank for now, and do a fishless cycle in another tank. You could buy a cheap five-gallon tank, fill it with Prime-treated tap water, and stick in a cheap sponge filter. If your tap water has 2 ppm ammonia to start with, that's enough to get the fishless cycle going. Once the ammonia starts to drop, you'll need to replenish it, perhaps by doing a water change from your ammonia-laden (but prime-treated) tap water, or better, by skipping the water change and adding a small amount of pure ammonia -- you can read up on all this in the posts and articles on fishless cycling. It will take a while for the small tank to cycle (maybe a month or more), and during that time, keep using the ammo lock in your main tank to protect your fish. But once the small tank cycles, you could do a large water change in the main tank (avoid using ammo-lock in the new water), and then add the cycled sponge filter into the main tank. This would result in a much more controlled and less stressful fishy cycle in the main tank, I would think.
If the fishless-cycle-in-another-tank isn't feasible, you still might want a fractional dose of the ammo lock, and test your ammonia daily. Someone else can probably better recommend what the ammonia levels should be during a fishy cycle, but I'm guessing you want something in the range of 0.25 ppm to 1.0 ppm, depending on how hardy your fish are.
