Compromise does indeed involve two people, but unless we're missing a large chunk of the story here, it's General Jinjur's husband who isn't compromising, not her.
Seriously, it is completely, 100% unfair to pull the rug out from under someone by changing your mind after a decision has been made, with too little notice to really reach a new compromise, and then just insist on getting your way. I'm guessing that if Jinjur's husband had come to her and said, "Honey, I'm really having second thoughts about getting rid of the fish tank. I know we agreed, and I know we're about to move, and I know that you've had a really hard time recently keeping the Nom away from the tank, but can we talk about how we might be able to keep the tank after all?" this thread wouldn't exist.
I also don't think it is at all fair to say that Jinjur is "shooting down" suggestions when she gives reasons why they won't work. Not having space, not being able to keep sufficient eye on the Nom and still be able to do anything else, and not wanting to pull him away from the fish tank three dozen times each day are all entirely reasonable answers to many of those suggestions.
Jinjur, has your husband said why he objects to having your fish live in multiple small tanks rather than one big one (which is what it sounds like your original plan was)? Has he given you any sort of reason for his sudden change of mind? If there are some underlying reasons in there, it would be worth finding out what they are -- it will make it easier to discuss the situation if you have a clear picture of everything that's going on.
But, in the end, you were operating under an agreement that you thought was set. Your husband changed the parameters of that agreement at the last minute. The onus of finding a solution that you both can live with really is more on him than on you, and I think it would be entirely reasonable to have a discussion with him to that effect. In other words, you lay out your requirements for "a solution I can live with" (which were undoubtedly considerations in the original agreement), and you ask him how he wants to work with those requirements. It doesn't really matter what he chooses to do, at this point, as long as your basic requirements are met.