I got my first mice in March of 2018. I made a lot of mistakes at first but luckily I learned fast and got some basics right!
First: Never house males together! Bucks get very territorial and while they may be friendly for a while, there is an extremely high chance that they will eventually begin to fight. This is sometimes only small bites but you can find horrific pictures of injured mice if you search. Intact bucks can be kept with female ASFs (African Soft Furred Rats) and neutered bucks can be kept with does. Neutering is a very risky procedure since mice are so small and it's hard to find a vet to do it, so it's genuinely just easier and safer to keep bucks solo.
Second: Seed mixes are awful for mice. Mice don't know what's healthy and will just eat what tastes best. They'll eat all of the seeds before they even touch the balanced lab blocks in a pre made mixture. I feed my girls Oxbow Adult Rat because it doesn't have corn (a common alergen) or cane molasses (unnecessary sugar meant to attract the animals) and they love it. I supplement with seeds scattered about the tank every couple of days and fresh veggies daily.
My current set up is a 40 gallon breeder fish tank. It's 3 feet long and 18 inches wide with a height of 16 inches. I'd love to upgrade to a 75 gallon in a few years once I have room.
My substrate is 5 bricks of eco earth and some moss. I used to use a brick of exo terra forest moss and might go back to it. It's more affordable than the sphagnum moss that I can buy in person but the trade off is I can only find forest moss on Amazon for some reason. This mixture is great because the mice can dig intricate tunnels that easily hold their shape. I constantly see the girls disappear on one side of the tank and then reappear from a hole two feet away!
They also get tons of things to hide in and chew on. Cardboard boxes and tubes get banished to the Mouse Shredder. These little ladies love destruction!
Bambi: Named so because I thought it was cute. This one poops like crazy. The other mice might poop on you, but this one will within the first minute without fail! If I hear a squabble going on, Bambi is probably involved. She started out with pure siamese markings (with the wrong eye color) but ended up becoming variegated silver.
Stimpy: Named so because I made my partner pick her out and name her. I wanted him to have a mouse that was sort of 'his' in a way. She's a little finger muncher! She WILL put her mouth on you if you reach into the tank and she's out and about. She won't break skin but will jump to get you if need be. No clue why she does this but at least it doesn't hurt. Stimpy is one of the more prolific tunnel diggers. I believe she's a silver broken marked. Her markings are suble but definitely there.
Pocky: Named so because her tail is black except for the last half an inch, which is pink. It looks like a pocky stick! She's my fattest mouse. Super active so I'm not super concerned about it, but she does weigh like 10g more than the other mice. She started as a black self but she slowly got white going down her spine and has little flecks of white, sort of like a reverse variegated.
Pinky: You know why she's named this. A friendly girl! She's always awake and running around, definitely becoming one of my all time favorites. Sits in your hand pretty well and isn't constantly moving. I have no idea what color this girl is. She's sort of like a really dark agouti. She's dark brown but has a really orange mix in her underbelly and subtly through the rest of her coat.
The Brain: You also know why she's named this. This little lady is a scaredy cat. She's surprising friendly and easy to pick up for a mouse that freezes if your shadow touches her. She bolts really easy when she's in the tank, too, but won't bolt when being held thankfully. Brain LOVES digging tunnels. I'm super confident that she's an argente color.
Blossom: The one that would sleep anywhere. Seriously, everybody else sleeps in normal spots but I would find Blossom sleeping on top of random cardboard boxes I had thrown in the tank. She would bury my hand in aspen chips when I was first trying to tame her and Buttercup. She ended up having some weird complication with her legs. She couldn't use her back legs and went on medication as the vet thought her spine might be inflamed. She seemed to be doing well but randomly died halfway through treatment, probably in late August 2019.
Bubbles: Sweet Bubbles. I don't know what her personality was really like, but she was curious and let me hold her even though I had just gotten her. I didn't know anything about small animals when I got my first mice and when I look at pictures of them the day I got them I can't believe I couldn't see how bad they were. I got her on a Saturday and she died Monday night while I was asleep, probably from salmonella.
Buttercup: My favorite mouse of all time. She was always trying to climb up my arm when I reached into the tank and loved running from one hand, up my arm, across my shoulders, and down the other arm to the other hand. Besides the white mark on her eye she was pure black. She passed unexpectantly from old age in December 2019.
Billy: She was a really 'standard' mouse. Liked to chew stuff and beg for treats. She was the dominant mouse for a long time and constantly groomed all of the other girls. I would put them in their holding tank for cleaning and she would go to eveybody and give them a few quick licks before moving on to the next. She got old and started slowing down, got a small cut on her stomach and in her old age it just didn't want to heal well. She died a couple months later in March 2022.
Mandy: My singing mouse. She was constantly making little noises. This is usually related to illness but the vet didn't find any kind of URI and said she just liked making noises. She was a nest builder and would play with any tissue paper I threw in the tank. A broken marked pattern with gold coloring. After slowly becoming weaker she died of old age in July 2021.
Bessie Named so because she looked like a little cow. At the pet store I worked at we only sold male animals and didn't accept returns of live animals from other locations. Someone at the other store told this customer we would take it and it was late at night and he was being a bit of an ass so we just took the mouse. Since she was female we didn't have a UPC for her and had to return her as dead. He said she was mean to his other mice but we thought he did something to her, possibly tried to feed her to a snake.
She was really jumpy. Like could barely look at her for the first month I had her jumpy. She bit my coworker before I brought her home and bit Billy the first time I tried to introduce her to the others. I managed to successfully introduce her to the other mice on December 18th. The first time she let me hold her for an extended amount of time was the day after. I immediately took a picture!
Bessie died unexpectantly in April 2021. She had no signs of illness and had been getting along with the other mice.