the only foolproof way I have found to keep my vanda roots healthy is to grow them bare-root (hang them from a wire in the open air) or in baskets with no media. Soak every day for at least 5 minutes.
Some people do grow them in pots or vases but in those situations root rot is possible if conditions are not spot on. More light and warmth may help if you want to keep trying with the vase method.