The plants will become food but the easiest way, if you have space is to cheat and grow your plants in pots. Have 2 or 3 your show tank and grow on 6 or 8 in your plant tank so that you can rotate them. If you have a deep tank, switch the plants when you do a water change, otherwise you will need a snorkel to reach the bottom! also check that you are giving them enough of the right foods. If their dentition changes, so does there diet; mature fish will eat such things as unsalted almonds!