It's best to use these to turn a decent amount of Guppies into Star Guppies, and use them in conjunction with the Starcatchers, as they will turn the Stars into Diamonds, making the $5 profit from Gold Coins to Stars into a $165 profit from Gold Coins to Diamonds. However, one must be careful with how many Starcatchers there are in the Tank, or else there may be more than can actually be feed. A good balance would be about 3 Star Guppies per 2 Starcatchers.