Can a tank cycle without a filter?

[Mint]

So, I have this betta tank I’m cycling. Anyways, I got it set up a while back, but my filter was faulty, so I had to order a new one. I left on a week-long vacation before I could get the filter. When I came back, green algae was growing in the tank. I’ve been checking the ammonia for about a week since, and it hasn’t climbed yet. However, nitrates are slightly above 0, I think around 5.0. This tank has plants that I planted before the cycle, so that may have contributed, but the parameters look like they show a cycled tank. Can I finally move my betta over from his other tank?

 

[Byron]

If you have reasonably fast growing plants, and floating plants are ideal here, you will not see a "cycle" with one betta. Provided the plants are growing. Ammonia and nitrite should be zero always, and nitrate as low and close to zero as is possible.

Did you add ammonia initially? I wouldn't with plants, so this is not suggesting you should. Just wondering.

 

[Colin_T]

The plants and algae use the ammonia and keep the nitrite and nitrate down.

You can put the fish in the tank and just monitor ammonia levels. If you have lots of live true aquatic plants that are growing well, then you probably won't need a filter for one fish.

Beneficial filter bacteria grows in dark areas on hard surfaces in oxygen rich water. Filters are the most common place for the bacteria to grow but they also end up on the glass, ornaments, gravel and plants, just in much smaller numbers.

 

[Mint]

Well, that’s good news on the betta: I need to move him for another tank. The filter is a HOB with adjustable flow, since I don’t like sponges, and since I already brought it I’m going to keep it in. Dad told me it was probably cycled, but I came here to check.
I did add a few fish food flakes once I had the filter in the tank, per his advice, but those seemed to not do anything to the ammonia: I didn’t even see a spike. It stayed continuously at zero. I can keep his old tank open for another week or two if a spike comes, so I should be good if it turns out the tank wasn’t cycled at all.