I have 6 of the silver dollars in a 125 liter aquarium. They co-exist wonderfully with 4 kuhli-loaches, and 3 algae eaters. Four of the six silver dollars (3 years old) that I have are about 13 cm long and are showing some pretty weird, but quite entertaining characteristics. They move up to one another very gracefully so that they are parallel to each other, head to head, tail to tail. They then begin to shimmer up against each other (abdomens touching) so that one fish, by the time they're finished, is nearly horizontal to the tank floor. It's almost like they're mating, and of course that's what I thought at first, but since all 4 are males, this just can't be true. Also when doing this, the Dollars develop two large black spots on both sides, one just behind the eye, the second vertically below the first, just up from the pectoral fin. The tips of the anal fin, dorsal fin, and especially the tip of the tail all turn black before, during and after doing this. The other 2 Silver Dollars that I have are a little younger (2 years old), they're about 8-10 cm long and are beginning to look like they may be females! They haven't, as of yet, begun to show the same characteristics of the others, but are approaching the same size as the other 4 when this all began. The difference between the males and the females, for those of you that need to know, is subtle, but the anal fin on the male is a little larger on the bottom and comes to more of a curve, wheras the female's anal fin is less long, and more pointy. Their main diet consist of Nutrafin Max (large flakes), 3 times daily. They also have a taste for shelled partially boiled peas and partially boiled romaine lettuce, but their favorite snack by far is the inner most soft part of a baby zucchini (near the seeds). I highly recommend these fish to anyone, beginner to expert. They do like to have more than one of their own species though, 2-6 +, depending on the size of the aquarium. Mine naturally paired up in just a short period of time, shoaling all together, or as pairs. They hate direct sunlight, so as I learned don't place them too close to a window. I've introduced other species to the aquarium and had no problem with them co-existing peacefully with each other. The dollars will seem a little freaked out at first, but after a day or two things get back to the norm. The only problem that I did have was that with the introduction of other species the silver dollars stopped growing altogether, so all other species, except for the dollars, kuhli's and algae eaters have been moved to my daughter's aquarium.
I have a group of large Silver Dollars, including the plain silver form and the spotted type, sharing a tank with a pair of large Red Hook characins (Myleus schomburgki) and a shoal of Clown Loaches. For those that have tried to keep them with plants, don't bother. They have eaten everything I have tried, including plants that are supposed to be unpleasant tasting. The only plants they leave alone are the three very large species of Crinum that are supplied by Tropica. For those that want to feed these very greedy fish, mine love cereals such as pasta and noodles, as well as pilau rice (without the sauce!). They of course eat all of the usual foods, especially green pleco flakes. I really do not understand why these vegetarian fish find it necessary to attack these foods like piranhas in a feeding frenzy. One odd observation is that they sometimes behave rather like marine fish at a reef cleaning station, staying absolutely still while a large Anostomus anostomus that also shares their tank nibbles its way over their surface, sometimes even scraping off some of the scales from their flanks. They also allow the Clown Loach to whisker them thoroughly, and will remain stationary for several minutes while they do this.
I've had two silver dollars for 15 years. I do not know how old they were when I got them and I'm wondering how long they can live. They reside in their 200 liter tank with a plecostomus and have always got along well with other fish. However, they always outlive them.
I have five Silver Dollars in my community tank. All were raised from 3 cm size about 6 months ago to about 10 cm long today, and still growing. They are timid creatures and tend to panic if you are doing anything drastic to the aquarium, however you can train them to be hand fed, particularly if you use bloodworms as food. Mine have a very strong schooling instinct, rarely being more than 5 cm away from another Silver Dollar - except during feeding time when its every fish for himself.
I have had Silver Dollars for about 4 years already, with 2 Jack Dempseys and 2 Firemouths. They get along great, with no fights or problems all. My fish they just keep to their own kind, so there are no problems.
I have had 5 silver dollars now for 6 years. They live well with my huge tin foil barbs, green severum, plecostomus and a few cory cats. I think their favorite thing to eat is zucchini, which I attach to the side and I seem to go through a whole one every week. They are very peaceful fish.