My tank is 50 gallon, 48" long. It has 20 glowlight tetras, 6 panda corys and 4 platys. Lots of low light plants such as jave fern etc. I have ordered a new T5 light and CO2 from ebay and just waiting for all that to arrive so I can plant with more options. I switched my filter media from a 20 gallon 1yr established tank and put it in this tank 2 weeks ago along with the platys that I already owned. The filter media is ceramic rings. 2 weeks ago when I set this tank up I also added some sponge to the filter and filter floss. Water stats were good until this morning. My ammonia is 0, my nitrate is about 20, but my nitrite was off the charts. HELP! How much water change should I do, should it be daily? So far I haven't lost any fish and I am worried they might start having issues. I just did about a 10% watch change. Will test again in an hour or so.
Your tank is still cycling. The good bacteria have finished eating all of the ammonia and converted them to nitrite. That is what caused the nitrite spike. The bacteria will now start to eat the nitrite and convert it to nitrate. That is the next spike you will see but will not be as deadly.
If your nitrite is off the chart I would do a 75-90% water change NOW. anything under a 25% water change isn't really going to do anything.
Due to the fact that you are cycling your tank with fish in it and that it is having the nitrite spike you want to be doing at least 25%-50% water changes daily. This is to keep your fish healthy. Nitrite is HIGHLY poisonous to fish and will cause them to get sick/die.
Use Prime water conditioner if available (it is twice to three times as potent as other products and works much better).
Prime conditioner detoxifies nitrite and nitrate for about 12 hours. It turns ammonia to ammonium.
With the low light plants you have the nitrite shouldn't be this high...but I guess you either have too many fish or too few plants to fully dodge the effects of the cycle. You could try getting more plants.
Do the water change, check the parameters. If your nitrite is above 1-2ppm...I would recommend doing another water change the same day for the safety of the fish. Not many fish can handle any levels of nitrite, especially this high.
Good luck and I hope all works well. I had the same thing happen to me. It will all calm down as soon as the bloom is over and you will be able to reduce the water change to about once a week. Always do more than 25% water changes. Weekly water changes should be around 50%.
Hope this helps!
I forgot to mention you are nearing the end of the cycle
so keep at it!
I let the filter circulate the water for about half an hour and retested. I would estimate the nitrite to be about .05 at present. I know that is unacceptable but for now I have to leave for work and can't do another water change until morning. I will keep at it until I have 0 nitrite then move to weekly water changes again. Thanks for the help. 
