Thanks for the help everyone

I have just put some stress coat in!

The tank is a juwel rio 300 which has a built in filter. The sponges etc are quite large (similar sized to the external ones of a similar capacity) so hopefully should be ok. The smaller tank had 0 ammonia,nitrite and nitrate so I reckon this larger one should be fine. But will keep testing to make sure of course!

Its not an established tank as I changed them from a smaller one very recently so I think its just a small cycle causing it but I did use the media from the old tank which was working all ok.