I'm having exactly the same issue trying to login - I'm guessing that as it's hosted on OP's own instance, our instances are not yet federated with his. Not really sure how to remedy that.
Edit: Managed to subscribe with the usual workaround - searched the community list for aquariums, not there. Searched again with [email protected], still not there. Waited a minute, searched again for 'aquariums' and it was there and let me subscribe.
Me too. I seldom posted on Reddit the last few years as I felt it got lost.