What kind of fish do you have? If it's goldfish or Koi. It won't matter what you try. I can't think of anything that would stop a fish from eating plants but... most tropical fish won't eat them.... or at least none that I've had.
silver dollars silver sharks corries red tailed shark and 2 catfish ! random selection of plants from internet unsure of names but even plants with hard leaves are being damaged . thankswhat fish, and what types of plants?
tank is 400 litres feedin flakes and pelletshow big is this tank? and what are you feeding them?