Nitrogen Cycle Stalled?

[Stu UK]

I have a small 25 litre tank (yes I know it is tiny, a bigger tank is on the horizon) with 11 Cardinal Tetras and a single Drawf Otocinclus. Temp is kept at 28c, pH about 7.2.

I am now nine weeks into the nitrogen cycle but my readings are a little weird and I wonder if it has stalled somewhere. I am using a brand new API test kit to take my readings and follow the instructions properly.

Until recently the ammonia was always surging quite high, easily hitting 3ppm or above. I brought this under control by frequent water changes and cutting down on feeding (I now feed a small quantity of high quality flake food once per day). I was never seeing any nitrites or nitrates.

For the past week or two, something has changed slightly. Now, my ammonia seems fixed at .5ppm and does not rise above. On two occasions I saw nitrites at .25ppm but within 24 hours this had dropped back to 0ppm with no change in ammonia. I have yet to see any nitrates. What could be causing the ammonia to sit at this level, while nitrites briefly appear, then disappear without any nitrates?

The fish themselves seem happy, no signs of distress and I haven't lost any. They feed well and school readily. The oto seems to be getting enough of the tank algae and has a big round belly.

Whenever I do a water change, I always use water conditioner. Also I only deep vacuum say a quarter of the gravel at a time. I have cleaned the filter foam once in old tank water, just gave it a few squeezes to get the worst out.

I am also fighting a dark green algae problem which is all over my fake plants and gravel. It is quite thick, strandy stuff and I wonder if this where the nitrates are going?

Any thoughts?

 

[Gvilleguy]

Hi Stu,

So this tank is about 6.6 gallons (I have to put it in my American brain UOM). Even for a fully cycled tank you are a bit overstocked, but it sounds like you know that.

How often and how big are your water changes? Even at 0.50 ammonia there is damage being done to your fish, but certainly not as bad as when ammonia was 3 ppm. So keep doing water changes as often as needed to get that number down.

As for the periodic nitrite reading, and no nitrates, I'm not certain what is going on there. You have the API nitrate test kit? Are you following the laborious instructions and whacking bottle #2 on the edge of a table a few times before shaking it up for 30 seconds? Since it has been nine weeks I would expect you to see at least some nitrates in there, if nitrites are being processed to zero like that.

 

[Stu UK]

Gvilleguy, thanks for your response.

Yes you are correct, it is about 6.6 US Gallons. A house move is on the horizon and the plan is to upgrade to a bigger tank once settled into the new house. In the meantime I need to crack this cycling problem.

I was doing 50% water changes every few days when the ammonia was high and I am now taking it as it comes. Just done a massive 90% change as the ammonia was starting to creep up from .5ppm while the nitrites/nitrates remained zero.

I am following the API instructions to the letter, although not going as far as banging the nitrates test on a table!

Just tested my tap water and results are as follows: pH 6.4, Ammonia 0ppm, Nitrite 0ppm, Nitrate above 0ppm but nowhere near 5ppm. Is it normal for the pH to increase from 6.4 to 7.2 in the tank? Also, it seems nitrates are present in my tap water, but something is consuming them in the tank, probably the algae. I am going to try keeping the tank lights off as much as I can to see if it stops the algae.

 

[snazy]

It is normal for the ph to increase in the tank. My tap water ph is 6.6, tank water is 7.4 in three of my tanks. Once the tank has cycled, the Ph should settle to a constant level.


Edit: Don't touch the filter media while the tank is cycling!!!Don't wash the media for a few weeks after the tank has cycled too. If the water is not clear enough then the issue is that the water flow is inadequate for the tank, the tank is overstocked or you are heavily overfeeding. Once it's all cycled and going ok,start slightly washing the media once a month maybe.


P.S: You need to shake bottle 2 on the nitrate test for a minute before you test. Otherwise the test will constantly show 0-5 max nitates.