Well if the water parameters are fine then the tank will be fine for a while, but what parameters is he checking? Ammonia, low end ph, high end ph, nitrite, nitrate?
Generally it is 1" of fish per gallon, and a betta alone is 2.5" thus leaving only .5" for his 3 gallon. But then there's the matter of guppies being typically 1 fish per gallon. And if the fish can live together well there's is no real harm in going over a tiny bit as long as they got room and the parameters are not affected.
But then there's the khuli loach, which is a 4" fish when it matures and is waaay to big for a 3 gallon. While it may not be a problem now it will be in the future.
So I guess you're sort of both right.
But honostly you're at each others throat over fish?! This is why I don't like people, egos. And I'm not sure which sex has the bigger one. Now it seems to me one of you has a temper otherwise yall could talk it out civilly. So you could continue arguing and hope it comes a conclusion before it costs you the relationship or you could agree to disagree and say what will be will be.
But remember in the game of wills, there are no winners.
He checks ammonia, nitrites, nitrates and pH daily. And that's good to know. At least we can both be happy they're not suffering for now.
And being hot-headed is an entirely different thing from having a big ego. We both have vicous tempers, and that's one of the things I like about him, but neither of us are overly egotistical. However, we have taken some time out and we are now being a lot less childish and argumentative about things so we can try and work something out. At the moment I'm offering him a bigger tank for his fish, as I have a spare. We're just unsure how I'd get it to him, haha.
good luck with that.
I don't need luck, sweetie~
Breaking up with someone over such a little thing would be frivolous at best.