My pond is 5500 gal. I have about 40 koi and some are very large. The last several years I have tried every spring to put submerged and floating oxygenator plants in but the koi eat them or eat their roots. Last year I tried several ways to make floating islands for plants but they sank. I have a fairly large water fall and two large air stones in there to increase the oxygen because of the fish load. This year I'm thinking I'm not going to even try and put submerged oxygenator. I really love the look of floating water lettuce, parrot feathers and water irises but I end of just wasting a lot of money. They also disturb my lilies. Anyone have any suggestions or tried and true solutions? Thanks