Nitrites starting to pick up, when should I do a water change?
 

Ammonia is starting to decrease so I'm assuming Nitrites will start picking up, when should I do a water change and what percentage?

Can you post the numbers for ammonia and nitrites?

How have you been cycling it?

Ammonia .25 down from .50

Nitrites .15

With fish, my signature should tell you which ones.

It's nothing but water changes when you cycle with fish. Get moving. start with about 20%, recheck and do more if they're still present. Your life now revolves around keeping those fish alive. It WONT hurt if you add a touch of superbac w/ each water change, yes its nitrifying bacteria and will help in a short time.Good luck

Agreed. When cycling with fish it's all about water changes. I cycled with fish (at the time I didn't know any better) and as soon as I saw a reading for amm. or nitrite is was instant water change on the spot. In my opinion none of my fish suffered during the process but it was very time consuming and I think I went through an entire API master test kit in the process, no joke. 20% is the volume I changed each time, and there were days on end where I did a 20% water change in the am and had to do another 20% in the pm. (Luckily it was a small tank and not a 100g plus). Stay on top of your parameters religiously and your fish will thank you :-)

If I keep nitrites and ammonia at 0, won't that stunt/stop my cycling process?

fish produce ammonia

As Burninator states, your fish are producing waste (ammonia) so your cycling progress will continue. Eventually your biological will increase to the point that it can handle the load your fish are producing. Once it reaches that point you can back off to once a week water changes. Keep on track with your water testing, performing water changes as necessary, and eventually your tank will cycle. Diligence & patience....:-)