Let's see... I personally have 11 bettas and a 15 gallon community tank and I supervise the care of my sister's betta and the 10 gallon don't-know-what's-going-into-it-yet tank at work.
What's stopping me from getting more-
- Money - although I did just get my tax return, so that's not as much of an issue at the moment
- Space - every available surface in my dorm that could safely hold a tank currently does, and the dorm I'll be in next school year is smaller than the one I'm in now. I'm working on switching to a rack system for the summer, though, and that may make space less of an issue
- Time - to a certain extent... It takes me around 1-2 hours to do water changes for all of the tanks, and it's a bit of a pain because I have to dump/get new water from the floor's bath/shower room down the hall.
- Running electrical cords - I have enough outlets to safely run all of my tanks, but I'm still working on getting all of them organized so it's easier to work with and doesn't look like a mess.
- Moving - I need to move some or all of my tanks to and from school at least three times a year, and it's a major pain in the rear getting everybody cupped/bagged, draining and tearing down the tanks, transferring them to the car, and setting them back up.
- To a small extent - college regulations on tank size. While my school technically allows up to 30 gallons of tank volume per room, they don't really seem to care. I have around 45 gallons total at the moment and know a person who runs a 50 gallon in his room - no one's ever had an issue so long as we don't do anything stupid.
I'm lucky that my parents are pretty darn accepting of my hobby and that they respect that it's more or less a form of therapy for me. However, I'm fairly sure that my dear father is starting to think that I'm becoming the crazy fish lady