Cover the vase so no light gets in. Just allow light on the leaves.
Plants can tolerate a low dose of hydrogen peroxide, so I would clean the vase once in a while with pure H2O2 (just let it soak with the plant removed, then a quick rinse). You can dip the plant for a short time in diluted H2O2 (length of dipping is shorter if the H2O2 is stronger- but you will have to do some research for exact times and doses). Add H2O2 with every water change. Not much, though. Plants do not like too much. Maximum dose 1.5 ml/gallon.