UGH... Have I killed my cycle???

I am on my 4th week of cycling my new tank intended for freshwater shrimp. The cycle had been running like clockwork (I did a fishless cycle and periodically added ammonia and using a test kit, watched it cycle over the past few weeks). So yesterday, I decided to do a 75% water change to get my nitrites down, then add my shrimp today. I changed the water, (using Tap Water as usual) and then went about my day. I went out with some friends and when I came back home last nite around 7pm my apartment smelled "fishy". It had never ever done that after a water change. I was completely at a loss for words! I went to the pet shop down the street and asked for some advice. He brainstormed a few ideas like i had done too big of a water change, but then he asked if I dechlorinated the water before or after adding to the tank. I immediately realized i COMPLETELY FORGOT to add my dechlorinator at all yesterday. He said the chlorine could have killed my bacteria that processed the organic stuff to keep the smells down and thats why it smells now. He wasn't sure but I think his theory holds water Does anyone have an opinion on this?? Will I have to start all over?? :cry:

**Edit** I also needed to change the water cause my driftwood had leeched tannins into the water and it was pretty reddish. In addition to reducing the nitrites. FYI

Thats what I was afraid of ;( thanks

So another 4 weeks? Thats really discouraging

Thanks all. Yes a planted tank. I've had plants in it since the start. I'm assuming the smell came from stirring up some of the dead plant material (i've had some plant casualties lol). I added a tiny bit of ammonia to the water just now. I have to work the next 3 days so I don't plan on adding shrimp until at least the weekend. If my cycle is still working the tiny amount I added will be gone by tomorrow nite-ish. Thats how my cycle has been running so far. I'm really praying I didn't wipe out the BB, but we'll see Thanks again for all the help I"ll update in a day or 2.