Continual Mini Cycle

[slickery]

My tank has been cycling for about two weeks. Before this had occurred the tank had gone through a full cycle and had normal levels (0ppm amonia, 0ppm nitrites, <15ppm nitrates) for about three weeks with fish in, including adding a couple of fish as well in that time. About 2 weeks ago I noticed a spike in Amonia and Nitrites while testing the water. Something like .5 ppm amonia, .25 ppm nitrites, 10 ppm Nitrates. The nitrites continued to go up, and thew amonia continued to go down, then I lost a Danio. I posted on this board and got advice to do water changes to keep Amonia and Nitrites below .25 via small water changes. At the time I was <.25 ppm Amonia, and about .5 ppm Nitrites, and ~ 10 ppm Nitrates. I do about a 40% water change, amonia is almost 0 but not quite and nitrites are 0, nitrates are about 5. Crap!! SO I wait... the amonia begins to rise again, amonia gets over .25, and nitrites are a little over 0, Nitrates are still around 5. I change the water again,I let the amonia go a little it stays about .25 and nitrites rise up to about .38, I change the water, more nitrites are removed than amonia... rinse, repeat, etc... Below is a little info about the tank.

55g tank
Tetra Wisper 60 (running since tank was set up)
Rena XP3 (running since tank started recent cycling, added one day after noticing levels were off)
Also running an air pump with 2 stones to increase surface agitation

Fish (at beginning of recent new cycle, with cycle deaths in ()):
3 zebra danios (1 died)
1 bristlenose cat
6 corys of some sort
1 Crowntail Betta (Still living but starting to look ragged)
1 Rainbow Shark (R.I.P today)

Several Live plants - 7 or so (keeping nitrates down too much?) Currently Healthy

Please Help!!

 

[WILDER]

Are you rinsing the sponges at all.

 

[slickery]

I rinsed the bio bags in the whisper 60 in the water I took from the tank during one of the changes. Other than that I haven't rinsed in any of the other media.

 

[WILDER]

How long ago was that.