skimmer over flow

I’ve had a skimmer going for three weeks perfectly fine. It broke in quick and has been working but last week i took out my canister filter as for the past month I’ve been transitioning from that to a sump. Suddenly today it filled up completely in a matter of hours. I looked in the tank and...

Simmer overflow last night, didn't think much of it but decided to check ammonia levels this morning and it spiked to 2.0 from 0. since bacteria is established and went through the nitrite-nitrate cycle, would the ammonia harmless as in less toxic to fish??? I'll be doing a 50% water change...