I’ve got 4 angel fish in a 40-gal aquarium right now and they have clearly outgrown it. I’m going to upgrade to a 50-55 gal aquarium. But I have two acrylic tanks I’m looking at, one is 15″x36″, the other is not as deep much somewhat longer, 12″x48″. Both are 20″ high.

What is better for the fish?

1. The tank that’s not quite as wide, but a few inches deeper to the back, giving them a decent swim range in all directions, or

2. The tank that’s not as deep but much wider, giving them a longer swim range in one direction, but not as much range back to front?

(Ideally I would love to get a much larger tank like a 100 gallon 60″x18″ for example, but over the past 4 years I’ve been progressing from an original 10-gal (with 2 gold fish), to a 30-gal (mix of tetras and guppies), to the current 40-gal (just the 4 angels, that started as 1″ and are now 4″ each), and I’m not too keen on growing it too much larger all at once. I’ll get there… but just not now. And yes, I fully agree, larger tanks actually take less work to maintain.)

Would love to hear from experienced aquarium owners about the size options and which seems to work better for fish of this size.

Thanks!
There actually IS a formula, that generally says 1″ of fish per gallon, but I think it’s up to 1″ per 3 gallons for more territorial fish.

One of them is actually 6″ big as has established herself as the boss… and the other 3 are between 3″ and 4″. They are all a little territorial and have their spats.

I was thinking that maybe the longer tank would give them more security for territoriality… if big momma is on one side and the next big one has declared her territory 3′ away on the opposite side, they’d be happier than being 12″ apart.

Based on the old saying, fences make for good neighbors, I wonder if they make fences for fish tanks?

LOL.