I also feel for this guy. It's not like they were going to lose their house or car because of two 20gal tanks. You'd hope she would at least be willing to compromise, if not tell that man to run! Run for the hills!!! Because that will not be a successful relationship, one party will end up miserable... Likely him by the sounds of it..
I mean, I told my ex he couldn't buy a few things - but there was reasons - usually decent ones. And I never ever made him get rid of something he owned just to please me, otherwise we wouldn't have our silver dollars.
I'll give you some examples of things I said he couldn't buy - and my reasoning behind them.
First thing that comes to mind is alcohol and its not that he couldn't buy it, just not too much. I didn't like him drinking too much because he was an alcoholic when we first got together and a little abusive. So while I didn't mind him having a drink here and there, I didn't like him being sloshed because of his history with it. And he was fine with it and agreed that he's a better person when not sloshed so that was a win/win.
I also wouldn't let him buy fish unless he'd done his research on them, when we first got into fishkeeping he brought silver dollars with no knowledge of what they were and I wasn't letting another scenario like that happen again. I'm still not happy with him and its been like 8½ years since we got them lol
Another example is when he wanted to buy another car. We already had two cars and the real estate wouldn't allow a third and I wasn't getting evicted over a car - especially since we already had two of them. I was willing to compromise however and if he got rid of a car he could buy another.
Otherwise, as long as the bills were paid and the savings saved I didn't care what he spent his money on.
He let me buy expensive shampoo so why should I stop him from having his luxuries? It only seemed fair.