It also depends upon what type you have. It's my understanding Red Hooks are some of the largest growing. I have 6 common Silver Dollars in my 180 and from what I read, they get to about 6-8 inches on average. I got them from someone else so I'm not positive about their age, but my guess is they are about a year or so old. I've had them for several months and they are growing, but not rapidly. The are currently about 4-4.5 inches in size and they eat just about anything I put in the tank. Sinking pellets, wafers, bloodworms and even live earthworms are all snapped up by these guys. I also add Romaine lettuce and/or spinach leaves about once a week and they devour them too. I seem to remember reading something about them needing a larger tank due to their skittishness. Mine dart all over the place if I make sudden moves. My experience with SDs is about five months, so I'm sure there are people on here with much more experience than me. For what it's worth, I enjoy watching them, but can't help but think they have a pea for a brain by the way they act. My guess is a 90 is big enough, but if you have one of the larger species, you may need to rehome down the line.
