Silverdollars have the tendicy to reach about 6-8''. My best bet for a 35 gallon would be 1-2 silverdollar/s. But then agian they love to school, so I'd go higher. A 55 would be good for 5-6 silverdollars. I may rearrange the tank for some more silverdollars, once I get rid of my oscars. As to the original poster, I wouldn't add any more fish.RedBellyRhen;4131172; said:Aww they kinda look like piranhas! How many of these would I be able to keep in a 35g? Also would I be able to keep some glass cats with them? If so how many?