I have two ottos in my 10-gallon community tank. There is little if any visible algae. I put in sinking algae wafers when I feed the other fish, but they don't go over and eat them like the other fish do with their food. The wafers are always gone later in the day when I get home, but I have no idea who is eating them or if they are just dissolving. Should I be concerned or is this normal?