I have two goldfish in a smallish tank (about 6L). Ive had them for about three years. One is larger than the other, about 5c. and pretty bulky. The other is small and thin, with thin long fins, The small one is sick and the tips of its fins are black. Every now and again i find it floating on top of the water looking pretty sick. This has happened before, a few months ago, and the fish recovered. Now it is sick again. Does anyone know if there is anything i can do to help it recover?
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