Bioload too high?

[Frogs]

Ive had 4 axolotls in a 40 breeder and it was cycled. I have a 30g aquaclear HOB filter and two sponge filters. I cleaned the two sponge filters two months ago which caused the cycle to mess up. It's been 2 months and it still hasn't fully cycled. I have nitrates but its not at zero ammonium. The axolotls have grown fast and I am now suspecting that the bioload might just be too high for the filters. Can anyone give me their opinion on this?

 

[TheFishGuy1999]

alg if you have nitrate it means you must be finishing the ammonia cycle but it could have been caused because you added the axolotls to quickly and didnt give the tank enough time to cycle or the cycle had finished but then you have added all 4 axolotls at once which destabilizes the bioload and the tank has to start the ammonia cycle again