The leaf tip burn is likely caused by the fans blowing directly on the plants.
Follow stumps advice on watering. He is bang on. Don't try to measure your watering needs, do it by feel. Water thoroughly, on an as needed basis. Ideally you want to water every other day, but sometimes the plant or soil doesn't allow for it. In the future you could amend your soil mix to improve drainage, but for now I'd just focus on proper technique.
What is happening is that your roots are always wet and this is preventing oxygen from getting to them (It could also lead to root rot
). So despite the small amount of water you are giving them, they are over-watered. A thorough watering will actually help to draw air into the soil.
Hope this helps.