I recently started looking after a female goldfish (Grogu) whose previous owner couldn't continue looking after.
Unfortunately, for the past 2-3 weeks I've only been able to keep her in a small 20L fish tank (a 35L fish tank is on its way but I'm afraid that's as large as it can be due to lack of space).
I am new to fish keeping so I started reading about the nitrogen cycle and the "new aquarium syndrome". Unfortunately, I'm struggling to balance the aquarium. Here is my process:
Fill in the 20L tank with tap water. I add Tetra AquaSafe product and a 1.5L bottle of distilled water and 5ml of Tetra FilterActive Bacteria.
The water filtering is done through a sponge filter (2W), which size is the recommended for this tank size. The plant is artificial.
Every 2-3 days I do a 30-50% water change (depending on how bad the water test results are).
Tank after 2 week of water cycling (pictures taken immediately after a 50% water change ):
After 2-3 days from the last water change I observe:
The Ammonia levels (tested with API ammonia test strips) is zero. I understand this means the bacteria that turn Ammonia into Nitrite are doing their job.
The Nitrite levels spike after 2-3 days to dangerous levels (>1ppm).
The Nitrate levels remain 20-30ppm.
The issue appears to be the lack of bacteria that would turn the Nitrite into Nitrate. Also, the presence of brown algae (diatoms?) concerns me as well.
Should I continue water cycling the tank? Will the Nitrite eventually stabilize?
With each water change, should I continue to add the Tetra FilterActive product?
Should I clean the brown algae (diatoms?) from the pebbles and plants? are they dangerous?
When the Nitrite levels get dangerously high, I've tried using Seachem Prime Concentrated Conditioner with little success.
Thank you very much for all your help in advance