I think they are good for their size. They were the perfect size for our Betta aquarium. I put a few in 3.5 gallons when they arrived and even after a month I haven't noticed any change in the color of the water, also the pH is the same. The fish seemed to like them and shortly after they were added he even built a little bubble nest. I'd say it's worth it, maybe I just need to add more.
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