I had 11 running at once a while back, of those 4 were salt! To much work. What I lack for quantity I make up for with quality now. Some changes in who lives where are happening this weekend and will result in:
210- 2 pacus, a pleco and an oscar
125- tilapia and lots of others
75- goldfish (3 of them)
75- cold water marine
30-breeder guppies
I have grow out and QT tanks that get set up and taken down as needed.
30, 10, 20x 2, 16 x 6. The 16's are actually divided 55 gallon tanks. At the moment the 30 has some giant danio fry growing in it.
I manage by cleaning when I can. Some weeks they all get done at once, other weeks I do a tank when I get a chance. I have 2 planned for cleaning today. All tanks are tracked on a spread sheet, nitrates never get over 10 and water changes are done at least every 7-10 days.