You were right on!! Tonight the ammonia is barely at a trace and no nitrites. I did another 40% water change and more vacuuming. The two cardinals are going back to the store. Soon I hope my little fellas will be happier with all the same species in the tank. I will replace the cardinals with neons.Yes, skipping a day or even 2 is fine for your fish & better for your water quality. Keep up the vacuuming! You'll see good results very soon!
I noticed something I'm not sure I like. There were two teeny tiny snails on the glass. I just don't like it because I know as a past med tech freshwater snails carry schistosomiasis. Granted this is in other parts of the world. I suppose the chances are slim, but there are schistosomes in the US causing "swimmers itch".
Could the snails be beneficial? Will they go bananas and multiply over night??