To add to what Jesnon said - if you have Malawi cichlids, you will have a high pH. Ammonia is more toxic at high pH so you really need to get it low by as many water changes as necessary and as big as necessary. It is fine to do a 90% water change if that's what it takes as long as you warm the new water to the same temp as the old water so you don't shock the fish.
To give you an idea, at pH 8.0 and a temp of 25 deg C, even 0.5ppm ammonia is toxic.
Is there any way you can return the fish to the shop and do a fishless cycle? Maybe ask the shop if they'll hold the fish for a few weeks for you?
Zeolite is not really a good idea. Yes it will absorb ammonia but if you remove it all this way there will be none left to feed any bacteria so they won't grow. Then when it gets full there will be nothing removing ammonia and the level will rocket.
If the AM Guard you refer to is one of those products that detoxifies ammonia, bear in mind that the effect lasts only around 24 hours.
The bacterial booster probably won't do much as most of them either contain dead bacteria and/or the wrong species on nitrite eating bacteria. But you might be lucky and the one you used might have an effect.
If you want to keep the fish, you are in for some hard work I'm afraid. Test the water a couple of times a day and do water changes to keep the ammonia low.
The good news is that nitrite is less toxic at higher pH. Once you get to the stage where ammonia stays low but nitrite is high, the fish are in less danger than in a tank with low pH. The effect of nitrite can be mitigated by adding plain salt to the tank and Malawi cichlids are fish that can cope with salt. Once you get to that stage, I'll let you know the amount to use.
And just to add that I'm assuming you have hard water with a high pH because you have Malawi cichlids.Iif you have soft acid water, they will not do well.