Oncidium has brown tips on leaves and black spots

[trafficdonna]

Hello, I am a brand new member. I have a Oncidium that I won at a raffle at local orchid show. It has bloomed twice for me in the two years that I’ve had it. However it has developed brown tips on the leaves and some black spots. What is this and what can I do about it? I water from the bottom by soaking planter in lukewarm water for 20 minutes once a week.
Thank you for any help you can give me. I also raise phaleanopsis orchids and use the same watering technique. They are all planted in bark.