Help! What happened?!

Okay here it is. A few days ago I got my first Nitrate readings. My levels were 0 Ammonia, 5 Nitrite and 5 Nitrate. This is great, I'm thinking that soon the Nitrite will drop and then I will be done! I tested a few days later and got 0 Ammonia, 0.25 Nitrite and 0 Nitrate... I thought this was very strange as before I had a Nitrate reading. I haven't done anything differently, been dosing a few fishfood flakes every 12 hours. Well, last night my readings are all 0. PH is 7.2. I have a Nitrate sponge in my filter and it is a planted aquarium, should I remove the Nitrate sponge? I am very confused! Has my cycle just completely died off? Is that even possible? I did a test to see what was happening. At lights off last night I dosed my fish flake as I have been. I waited until I went to bed (6 hours later, I got stuck watching a film) and took a test. I had 3ppm Ammonia. I tested again just now and my Ammonia has gone completely, but I don't have a Nitrite reading? The aquarium has been cycling for about 3 weeks now, what should I do?

Dan.

 

If the nitrate sponge elimanates nitrates , I would remove it, that could be it or the live plants, plants use nitrate as a food (fertilizer).

 

Okay thanks for a speedy response. As the nitrate sponge sits below another sponge, would you replace it with another filter sponge, to collect bacteria? Or just leave it empty?

Dan.

 

Yes, I'd put another sponge.

 

Okay I removed the Nitrate sponge and replaced it with a fine sponge. Washed it in the water that came out of the sponges whilst the unit was out, and then quickly washed it through. Added it in and will test the water later on tonight. Hoping nothing bad has come of this. Just to clarify when it is cycled, and before I add fish, I need to do a large water change don't I? About 50-60% or more?

Dan.