OK, so I went into fish keeping way too fast with almost no knowledge. I will give a short rundown of what happened in my tank.
I got a 5 gallon (19 liters) tank and a silver molly and a leopard longfin danio. I found out I need at least a 10 gallon (38 liters) so I got that both were Topfin Starter Kits. Decided I want more fish; so I got a neon tetra, gold dust molly and an Otocinclus catfish. I found out my danio was bullying my tetra, so I found out all the fish I had were very social creatures, so I got a zebra danio and a fish I thought was a tetra when it was actually a White Cloud Mountain minnow.
I overfed my fish and my tank became dirty, so I did a 25% water change. My catfish and gold dust molly died, so I removed them from the tank. I realized my mollies mated, so now I have 3 baby mollies. Found out about the ammonia spike and freaked out, and I bought a floating baby tank thing for the babies and a Tetra Whisperer Filter for the ammonia levels along with putting an absolute heck ton of conditioner and stabilizer and Stress Zyme. Ammonia levels still didn't go down, but my fish were acting normal. New filter arrives, so I put it in and took the old one out. I was freaking out, looking stuff up constantly this entire time and found out about the biological filter. Ammonia levels still didn't go down.
I added small amounts of salt to help because I saw it in a Youtube video. That still didn't work, so I decided: hey, let's put the old filter back, but keep the new one in two so now I have two filters. And I did a 50% water change, not 10 minutes ago from posting this.
My question is what the actual heck am I doing wrong? Help me please.