@susan ingram try testing the water that comes out of your RO/DI for ammonia, start there first.

If you are using an API ammonia test kit, I’d highly recommend getting a different brand, as that test kit is known to be terribly inaccurate and often times will show false positives. If your newly made RO/DI water show ammonia then chloramines are likely present. (You can test your tap water too, if it has ammonia in it then it’s a pretty safe bet it’s got chloramines in it and you’ll need to use a different type of carbon block in your RO unit to properly scrub the water free of them).
First off it’s ok to feel the way you are feeling, if you didn’t feel bad about what happened that would be a problem. There are lots of us here that have made mistakes that have had terrible consequences for our livestock too, you are not alone. All of us have learned hard lessons in this hobby one way or another. So let’s find the cause and fix it so it never happens again. It’s wonderful to hear that you spent a couple years studying this hobby before jumping it with gusto, that‘s awesome and will help you out in the long run, but unfortunately it doesn’t make reefkeeping any easier, especially at times like this. You’re not expected to know it all, especially how to act in a crisis situation. That only comes from experience. I’m sorry you are having a really really bad experience right now. So catch your breath and your bearings and lets find the solution to your problem.
First off removing the terracotta pot was a prudent decision, it may or may not be the cause of the ammonia but you’ve eliminated it from the equation.
Do you have any bottled bacteria for starting tanks? Like Dr. Tim’s or BioSpira etc. If you do I would go ahead and add a hefty dose to the tank, that would help boost the population of nitrifying bacteria in the system to help start processing the ammonia naturally.
Completely breaking down the tank may not be the best solution as you will be starting over completely from scratch and will have to restart the cycle completely.
I would also add some activated carbon to your filter somewhere if you have some. Not a whole ton of it, but a normal amount to help pull any possible contaminant out that may be the cause.