Some of my fishes are scratching themselves against the sand and driftwood. I thoguht at first they have a parasite on them, but when i look closer, there's nothing wrong w/ them. Checked their scales if somethings missng. But they're all intact. Feeding well. Just change the water and added some salt, and still doing it(scratching). Does this things happen to your fishes guys or there's a paraiste i don't know. If there is a paraiste, what should i do?