In that case, its definitely a good idea to dose a second time.
Actually, I get copepods from time to time from my tap. I have Cardinal Tetras but a few copepods seem to survive despite being in a bare bottom tank.
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Copepod also come in on the fish themselves. They probably eat the slime coat and its microflora and fauna.
Al
Al, A bottle of cold sake is the best except the PRICE!