I suspect a test kit error as that's very high. Which kit are you using? If a subsequent test bears the same result then do a water change (with dechlorinator) to get it below 5ppm as at that level it can actually prevent cycling.
I use the Sera test kit. I’ll test again in a moment and see if anything changes. If so I’ll do a water change as you have advised. So anything above 5ppm ammonia prohibits a cycle? As does chlorinated water.
Yes, high levels of ammonia inhibit bacterial growth - hence its use as a household cleaner. The chlorine in tap water is put in specifically to kill bacteria and it will wipe out any filter bacteria very easily, which is why we always use a dechlorinator for aquarium water.
I’ve done a 50% water change with dechlorinated water and got the ammonia down to around 3ppm now.
I’ll now continue with the article on ammonia cycling.
One question I do have is, do I continue to keep ammonia levels at 3ppm until nitrites have a zero reading? When do I stop feeding ammonia? Or does that never stop as long as I want the filter to continue to harbour the beneficial bacteria?
Dose with ammonia back up to 3ppm whenever it drops to 0. When you get to the stage where 24 hours after dosing, both ammonia and nitrite are at 0 the cycle is complete. At that point, nitrate will be very high and you should do a very large water change to reduce that before adding fish. If there is to be a delay of more than a couple of days between the cycle completing and stocking with fish continue dosing ammonia daily as without it all the good bacteria you've grown will die off.