These underwater plants cool the water much the same way a shade tree does. They are also useful as natural filters since they are planted in gravel and must take nutrients from the water. These plants also are great spawning media for goldfish. They should be selected for how they fit in to the landscape. Try to place them in the background so they do not obstruct the view of the water.
Lotus can be quite large if the full size varieties are given enough space and fertilizer.
They can reach up to four feet above the water surface with leaves 15-18 inches in diameter or more. Some varieties are smaller with leaves standing only a foot or two off the water and twelve-inch leaves. Bowl lotuses are going to have four to six-inch leaves that will grow six inches above the water. Underwater plants such as Anacharis or Cabomba are often called oxygenating plants. They provide oxygen during the day, but like any other plant, they use oxygen during the night.