I've got a 20g set up 7 days ago, and being impatient, I've filled it with 6 small neon tetras (around 1.5cm), 9 other unknown tetras (1cm long), 4 endlers and a small albino pleco (1.5cm). Also popped around 55 shrimps in there (rcs, chocolates).
I am using a Eden 511 canister filter (rated for 160 gallons per hour for my 20 gallon tank, or 8 times water turnover per hour) that has 3 compartments, 2 are sponges and 1 is ceramic ring. I have a cycled 10g, and I swapped all the ceramic rings from my 10g into the 20g filter. I thought that it would be enough to give my new 20g a jump start to cycling.
I bought the API test strips and have been using them to test the nitrites and nitrates (the 5 in 1 test strips doesn't test ammonia). For the past 3 days, I was getting some slight nitrite readings, and some heavier nitrate readings. The test strip colors aren't that clear, but I felt that the nitrite levels are acceptable as I have been doing a daily 30-35% water change with water conditioner. The presence of nitrates also assured me that the nitrobacter was doing it's job converting nitrites to nitrates.
This morning, I used my last API test strip, as usual, lowish nitrites (.5-1ppm) and some nitrates (20-40ppm). I did my 30% water change and headed out to the fish shop to get the liquid test.
I bought the API liquid nitrite test, and tested the water 4 hours after my morning water change. Nitrite levels were at 2-3ppm. I went into emergency mode and did a HUGE water change, maybe 80%. Subsequent testing showed 0.25 nitrite levels.
7 hours later, at 9pm, I did another water test, and it showed nitrite ppm at 2 again. I did another huge 70% water change and got it down to 0.25-0.5 ppm.
Is there anything I can do except for water changes? I've moved the pleco from the 20g to 10g to spread the bioload, and moved some rocks from 10g to the 20g. Would leaving the LED lights (no UV) on help in any way? Would adding an air pump bubbler work? I heard that a richer oxygen environment helps bacteria grow faster, I know the air bubbles have very little contact time with the water column, but would it help even just a tiny bit?
The tank is around medium-low planted, I'll attach a picture if that helps.